Creating an installer for an addin

November 30, 2017 by Erik W in Addin

In a previous post I created my Tesseract OCR client add-in. To test that it worked properly, I registered the client add-in using the debug output path for the assembly location. This allows me to debug the add-in but won't work on any other workstation. Therefore I need to package the add-in into an installer, which would place the required files in a consistent location I can reference when registering the add-in.

To create an installer you'll need the WiX toolset. You can then add a new project to the solution using the Setup Project for WiX v3 project template, as shown below. Note that can you create multiple installers within a given solution (which I'm doing since I have two different add-ins: client and event).

Anytime I add a new project to the solution I revisit the configuration manager. Since I can envision wanting to debug the add-in without any need to create an installer, I decide to create a new solution configuration named "debug (installers)".

Note the active configuration (debug) does not build installers

I leave the existing debug configuration alone and then modify the new one. The debug installer configuration should build all of the projects. Installing that output allows you to attach a debug session to an installed copy of the add-in. The release configuration is identical, except each project configuration is set to release.

The WiX project template results in one file being creating within the project: "Product.wxs". Before tackling that file, I immediately add a reference to the addin project and the WixUIExtension library. The UI extension library will allow me to create a custom UI navigation that prompts the user for the installation path.

I then created a file named UI.wxs and used the content shown below.

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
  <Fragment>
    <UI Id="AddinUI">
      <TextStyle Id="WixUI_Font_Normal" FaceName="Tahoma" Size="8" />
      <TextStyle Id="WixUI_Font_Bigger" FaceName="Tahoma" Size="12" />
      <TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="no" />
      <UIRef Id="WixUI_ErrorProgressText" />
      <Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
      <Property Id="WixUI_Mode" Value="InstallDir" />
      <DialogRef Id="BrowseDlg" />
      <DialogRef Id="DiskCostDlg" />
      <DialogRef Id="ErrorDlg" />
      <DialogRef Id="FatalError" />
      <DialogRef Id="FilesInUse" />
      <DialogRef Id="MsiRMFilesInUse" />
      <DialogRef Id="PrepareDlg" />
      <DialogRef Id="ProgressDlg" />
      <DialogRef Id="ResumeDlg" />
      <DialogRef Id="UserExit" />
      <Publish Dialog="BrowseDlg" Control="OK" Event="DoAction" Value="WixUIValidatePath" Order="3">1</Publish>
      <Publish Dialog="BrowseDlg" Control="OK" Event="SpawnDialog" Value="InvalidDirDlg" Order="4"><![CDATA[WIXUI_INSTALLDIR_VALID<>"1"]]></Publish>
      <Publish Dialog="ExitDialog" Control="Finish" Event="EndDialog" Value="Return" Order="999">1</Publish>
      <Publish Dialog="WelcomeDlg" Control="Next" Event="NewDialog" Value="InstallDirDlg">NOT Installed</Publish>
      <Publish Dialog="InstallDirDlg" Control="Back" Event="NewDialog" Value="WelcomeDlg">1</Publish>
      <Publish Dialog="InstallDirDlg" Control="Next" Event="SetTargetPath" Value="[WIXUI_INSTALLDIR]" Order="1">1</Publish>
      <Publish Dialog="InstallDirDlg" Control="Next" Event="DoAction" Value="WixUIValidatePath" Order="2">NOT WIXUI_DONTVALIDATEPATH</Publish>
      <Publish Dialog="InstallDirDlg" Control="Next" Event="SpawnDialog" Value="InvalidDirDlg" Order="3"><![CDATA[NOT WIXUI_DONTVALIDATEPATH AND WIXUI_INSTALLDIR_VALID<>"1"]]></Publish>
      <Publish Dialog="InstallDirDlg" Control="Next" Event="NewDialog" Value="VerifyReadyDlg" Order="4">WIXUI_DONTVALIDATEPATH OR WIXUI_INSTALLDIR_VALID="1"</Publish>
      <Publish Dialog="InstallDirDlg" Control="ChangeFolder" Property="_BrowseProperty" Value="[WIXUI_INSTALLDIR]" Order="1">1</Publish>
      <Publish Dialog="InstallDirDlg" Control="ChangeFolder" Event="SpawnDialog" Value="BrowseDlg" Order="2">1</Publish>
      <Publish Dialog="VerifyReadyDlg" Control="Back" Event="NewDialog" Value="InstallDirDlg" Order="1">NOT Installed</Publish>
      <Publish Dialog="VerifyReadyDlg" Control="Back" Event="NewDialog" Value="MaintenanceTypeDlg" Order="2">Installed AND NOT PATCH</Publish>
      <Publish Dialog="VerifyReadyDlg" Control="Back" Event="NewDialog" Value="WelcomeDlg" Order="2">Installed AND PATCH</Publish>
      <Publish Dialog="MaintenanceWelcomeDlg" Control="Next" Event="NewDialog" Value="MaintenanceTypeDlg">1</Publish>
      <Publish Dialog="MaintenanceTypeDlg" Control="RepairButton" Event="NewDialog" Value="VerifyReadyDlg">1</Publish>
      <Publish Dialog="MaintenanceTypeDlg" Control="RemoveButton" Event="NewDialog" Value="VerifyReadyDlg">1</Publish>
      <Publish Dialog="MaintenanceTypeDlg" Control="Back" Event="NewDialog" Value="MaintenanceWelcomeDlg">1</Publish>
      <Publish Dialog="CustomizeDlg" Control="Back" Event="NewDialog" Value="CustomizeDlg">1</Publish>
      <Publish Dialog="CustomizeDlg" Control="Next" Event="NewDialog" Value="CustomizeDlg">1</Publish>
      <Publish Dialog="InstallDirDlg" Control="Next" Event="NewDialog" Value="CustomizeDlg">1</Publish>
      <Property Id="ARPNOMODIFY" Value="1" />
    </UI>
    <UIRef Id="WixUI_Common" />
  </Fragment>
</Wix>

Next I modified the project so that there is a preprocessor variable for the source of files, the output is placed into an alternate location, and heat is used to harvest content. Below you can see those first two changes. This was done for all the project configurations.

In the build events I created a heat command that harvests the files into "Content.wxs"...

The full text of the command:

heat dir "$(SolutionDir)Output\ClientAddin $(ConfigurationName)" -dr INSTALLFOLDER -var var.sourcebin -srd -sreg -gg -cg AddinComponents -out "$(ProjectDir)Content.wxs"

Next I added a new file to the solution named "Content.wxs". This file will be replaced each time the project is built (the heat command above generates the content based on the output from the other project). The variable parameter matches the preprocessor variable name used in the project properties, effectively ensuring any future changes to the add-in will be included in the installer.

The last step is to update the product file. Within it I added all the usual manufacturer, product, and media information. Then I removed everything else (the default fragments provided by the project template). Instead I reference the UI and the add-in components generated by heat command.

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
  <Product Id="*" Name="CMRamble Ocr ClientAddin" Language="1033" Version="1.0.0.0" Manufacturer="CMRamble.com" UpgradeCode="05ff6529-a724-4eaf-a199-d920ef03bc20">
    <?define IFOLDER = "INSTALLFOLDER"?>
    <?define InfoURL="https://cmramble.com" ?>
    <Package InstallerVersion="300" Compressed="yes" InstallScope="perUser" />
    <MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
    <Media Id="1" Cabinet="ClientAddin.cab" EmbedCab="yes"/>
    <Feature Id="ProductFeature" Title="Installer" Level="1">
      <ComponentGroupRef Id="AddinComponents" />
    </Feature>
    <Property Id="ARPHELPLINK" Value="$(var.InfoURL)" />
    <Property Id="WIXUI_INSTALLDIR" Value="$(var.IFOLDER)"/>
    <UIRef Id="AddinUI" />
  </Product>
  <Fragment>
    <Directory Id="TARGETDIR" Name="SourceDir">
      <Directory Id="ProgramFiles64Folder">
        <Directory Id="CMRambleFolder" Name="CMRamble">
          <Directory Id="OcrFolder" Name="Ocr">
            <Directory Id="INSTALLFOLDER" Name="ClientAddin" />
          </Directory>
        </Directory>
      </Directory>
    </Directory>
  </Fragment>
</Wix>

All done! I repeated the process for the event processor plugin and then hit build. The result is an installer for each.

If I launch the client add-in installer I see the UI I defined in the UI.wsx file. It sequenced the user from the welcome dialog to the installation path dialog. Clicking next should ask the user where to install it.

It behaves as expected! The path you supply here is what you will use when later registering the add-in within the client, so it must be consistent across your organization.

Clicking next shows the ready to install dialog and an install button.

Once installation has completed, a new folder will exist on the workstation. It should contain all of the files harvested from the client add-in project. As the solution grows the installer should automatically keep-up with new references.

Contents of Client Addin installation on workstation

Within the client the add-in is managed by clicking external links on the administration ribbon.

Then click new generic add-in (.Net)...

Provide a name (this can be anything you want) and select the most appropriate path for your environment.

If you can click OK without receiving an error message, then you have a valid configuration (according to this workstation). Once the valid configuration has been saved, you must click properties to enable the add-in on specific objects.

The client add-in is intended for electronic documents so I enabled the document record type.

A quick test of the custom actions proves the installer worked successfully end-to-end.

You can access the latest installers here.

Automating the generation of Tesseract OCR text renditions

November 15, 2017 by Erik W in Integration, Imaging, Addin, Renditions

Although IDOL will index the contents of PDF documents, it does not perform its' own OCR of the content (at least the OEM connector for CM does not). In the JFK archives this means I can only search on the stamped annotation on each image. Even if IDOL re-OCR'd documents, I can't easily extract the words it finds. I need to do that when researching records, performing a retention analysis, culling keywords for a record hold, or writing scope notes for categorization purposes. In the previous post I created a record addin that generated a plain text file that held OCR content from the tesseract engine.

Moving forward I want to automate these OCR tasks. For instance, anytime a new document is attached we should have a new OCR rendition generated. I think it makes sense to take the solution from the previous post and add to it. The event processor plugin I create should call the same logic as the client add-in. If this approach works out, I can then add a ServiceAPI plugin to expose the same functionality into that framework.

So I took the code from the last post and added another C# class library. I added one class that derived from the event processor addin class. It required one method be implemented: ProcessEvent. Within that method I check if the record is being reindex, the document has been replaced, the document has been attached, or a rendition has changed. If so I called the methods from the TextExtractor library used in the previous post.

using HP.HPTRIM.SDK;
using System;
using System.IO;
using System.Reflection;
 
namespace CMRamble.Ocr.EventProcessorAddin
{
    public class Addin : TrimEventProcessorAddIn
    {
        #region Event Processing
        public override void ProcessEvent(Database db, TrimEvent evt)
        {
            Record record = null;
            RecordRendition rendition;
            if (evt.ObjectType == BaseObjectTypes.Record)
            {
                switch (evt.EventType)
                {
                    case Events.ReindexWords:
                    case Events.DocReplaced:
                    case Events.DocAttached:
                    case Events.DocRenditionRemoved:
                        record = db.FindTrimObjectByUri(BaseObjectTypes.Record, evt.ObjectUri) as Record;
                        RecordController.UpdateOcrRendition(record, AssemblyDirectory);
                        break;
                    case Events.DocRenditionAdded:
                        record = db.FindTrimObjectByUri(BaseObjectTypes.Record, evt.ObjectUri) as Record;
                        var eventRendition = record.ChildRenditions.FindChildByUri(evt.RelatedObjectUri) as RecordRendition;
                        if ( eventRendition != null && eventRendition.TypeOfRendition == RenditionType.Original )
                        {   // if added an original
                            rendition = eventRendition;
                            RecordController.UpdateOcrRendition(record, rendition, Path.Combine(AssemblyDirectory, "tessdata\\"));
                        }
                        break;
                    default:
                        break;
                }
            }
        }
        #endregion
        public static string AssemblyDirectory
        {
            get
            {
                string codeBase = Assembly.GetExecutingAssembly().CodeBase;
                UriBuilder uri = new UriBuilder(codeBase);
                string path = Uri.UnescapeDataString(uri.Path);
                return Path.GetDirectoryName(path);
            }
        }
    }
}
 

Note that I created the AssemblyDirectory property so that the tesseract OCR path can be located correctly. Since this is spawned from TRIMEvent.exe the executing directory is the installation path of Content Manager. The tesseract language files are in a different location though. To work around this I pass the AssemblyDirectory property into the TextExtractor.

I updated the UpdateOcrRendition method in the RecordController class so that it accepted the assemblypath. If the assembly path is not passed then I default the value to the original value which is relative. The record add-in can then be updated to match this approach.

Within the TextExtractor class I added a parameter to the required method. I could then pass it directly into the tesseract engine during instantiation.

If you expand upon this concept you can see how it's possible to use different languages or trainer data. For now I need to go back and add one additional method. In the event processor I reacted to when a new rendition was added, but I didn't implement the logic. So I need to create a record controller method that works for renditions.

public static bool OcrRendition(Record record, RecordRendition sourceRendition, string tessData = @"./tessdata")
{
    bool success = false;
    string extractedFilePath = string.Empty;
    string ocrFilePath = string.Empty;
    try
    {
        // get a temp working location on disk
        var rootDirectory = Path.Combine(Path.GetTempPath(), "cmramble_ocr");
        if (!Directory.Exists(rootDirectory)) Directory.CreateDirectory(rootDirectory);
        // formulate file name to extract, delete if exists for some reason
        extractedFilePath = Path.Combine(rootDirectory, $"{sourceRendition.Uri}.{sourceRendition.Extension}");
        ocrFilePath = Path.Combine(rootDirectory, $"{sourceRendition.Uri}.txt");
        FileHelper.Delete(extractedFilePath);
        FileHelper.Delete(ocrFilePath);
        // fetch document
        var extract = sourceRendition.GetExtractDocument();
        extract.FileName = Path.GetFileName(extractedFilePath);
        extract.DoExtract(Path.GetDirectoryName(extractedFilePath), true, false, "");
        if (!String.IsNullOrWhiteSpace(extract.FileName) && File.Exists(extractedFilePath)) {
            ocrFilePath = TextExtractor.ExtractFromFile(extractedFilePath, tessData);
            // use record extension method that removes existing OCR rendition (if exists)
            record.AddOcrRendition(ocrFilePath);
            record.Save();
            success = true;
        }
    }
    catch (Exception ex)
    {
    }
    finally
    {
        FileHelper.Delete(extractedFilePath);
        FileHelper.Delete(ocrFilePath);
    }
    return success;
}

Duplicating code is never a great idea, I know. This is just for fun though so I'm not going to stress about it. Now I hit compile and then register my event processor addin, like shown below.

I then enabled the configuration status and saved/deployed...

Over in the client I removed the OCR rendition by using the custom button on my home ribbon...

When I then monitor the event processor I can see somethings been queued!

A few minutes later I've got a new OCR rendition attached.

Progress! Next thing I need to do is train tesseract. Many of these records are typed and not handwritten. That means I should be able to create a set of trainer data that improves the confidence of the OCR text. Additionally, I'd like to be able to compare the results from the original PDF and the tesseract results.

Using Tesseract-OCR within the Client

November 14, 2017 by Erik W in Addin, Imaging, Renditions, Integration

In a previous post I showed how to generate OCR renditions via Powershell. The process worked quite well, and the accuracy is higher than other solutions. After that post I went to upload the powershell scripts to github and decided to re-run each script against a new dataset.

As I ran the OCR script I noticed a few things I did not like about it:

The script ran fine for hours and then bombed because the search results went stale
I must remember to run the script after each import of records, or no OCR renditions
I had to create a custom property to track whether an OCR rendition was generated

To overcome these challenges I'll need to write some code. Time to break out Visual Studio and build a new solution. So let's dive right in!

I opened up Microsoft Visual Studio 2017 and created a new solution with two projects: a C# class library for the add-in, and a C# class library for the Ocr functionality. Here I'm splitting the Ocr functionality into a separate project because in the next post I'll create an event processor plug-in. To make this work I updated the first project to reference the second and set a build dependency between the two.

Next I implemented the ITrimAddIn interface and organized the interface stubs into logical regions, as shown below. I also created a folder named MenuLinks and created two new classes within: UpdateOcrRendition and RemoveOcrRendition. Those classes will expose the menu options to the users within the client.

The two menu link classes look are defined as follows:

using HP.HPTRIM.SDK;
 
namespace CMRamble.Ocr.ClientAddin.MenuLinks
{
    public class UpdateOcrRendition : TrimMenuLink
    {
        public const int LINK_ID = 8002;
        public override int MenuID => LINK_ID;
        public override string Name => "Update Ocr Rendition";
        public override string Description => "Uses the document content to generate OCR text";
        public override bool SupportsTagged => true;
 
    }
}

using HP.HPTRIM.SDK;
namespace CMRamble.Ocr.ClientAddin.MenuLinks
{
    public class RemoveOcrRendition : TrimMenuLink
    {
        public const int LINK_ID = 8003;
        public override int MenuID => LINK_ID;
        public override string Name => "Remove Ocr Rendition";
        public override string Description => "Remove any Ocr Renditions";
        public override bool SupportsTagged => true;
    }
}

Now in the Add-in class I create a local variable to store the array of MenuLinks, update the Initialise interface stub to instantiate that array, and then force the GetMenuLinks method to return that array....

private TrimMenuLink[] links;
public override void Initialise(Database db)
{
    links = new TrimMenuLink[2] { new MenuLinks.UpdateOcrRendition(), new MenuLinks.RemoveOcrRendition() };
}
public override TrimMenuLink[] GetMenuLinks()
{
    return links;
}

Next up I need to complete the IsMenuItemEnabled method. I do this by switching on the command link ID passed into the method. I compare it to the constant value that backs my Menu Link Id's. If you look closely at the code below, you'll notice that I'm calling "HasOcrRendition" when the link matches my RemoveOcrRendition link. There is no such method in the out-of-the-box .Net SDK. Here I'll be calling a static extension method contained inside the other library. I'm doing this because I know I'll need that same capability (to know if there is an Ocr rendition) across multiple libraries. It also makes the code easier to read.

public override bool IsMenuItemEnabled(int cmdId, TrimMainObject forObject)
{
    switch (cmdId)
    {
        case MenuLinks.UpdateOcrRendition.LINK_ID:
            return forObject.TrimType == BaseObjectTypes.Record && ((HP.HPTRIM.SDK.Record)forObject).IsElectronic;
        case MenuLinks.RemoveOcrRendition.LINK_ID:
            return forObject.TrimType == BaseObjectTypes.Record && ((Record)forObject).HasOcrRendition();
        default:
            return false;
    }
}

The last two methods I need to implement within my record add-in are named "ExecuteLink". Here I'll hand the implementation details off to a static class contained within my second project. Doing so makes this code easy to understand and even easier to maintain.

public override void ExecuteLink(int cmdId, TrimMainObject forObject, ref bool itemWasChanged)
{
    HP.HPTRIM.SDK.Record record = forObject as HP.HPTRIM.SDK.Record;
    if ((HP.HPTRIM.SDK.Record)record != null)
    {
        switch (cmdId)
        {
            case MenuLinks.UpdateOcrRendition.LINK_ID:
                RecordController.UpdateOcrRendition(record);
                break;
            case MenuLinks.RemoveOcrRendition.LINK_ID:
                RecordController.RemoveOcrRendition(record);
                break;
            default:
                break;
        }
    }
}
public override void ExecuteLink(int cmdId, TrimMainObjectSearch forTaggedObjects)
{
    switch (cmdId)
    {
        case MenuLinks.UpdateOcrRendition.LINK_ID:
            RecordController.UpdateOcrRenditions(forTaggedObjects);
            break;
        case MenuLinks.RemoveOcrRendition.LINK_ID:
            RecordController.RemoveOcrRenditions(forTaggedObjects);
            break;
        default:
            break;
    }
}

Now I need to build the desired functionality within the solution's second project. To start I'll go ahead and import the tesseract library via the Nuget package manager. As of this post the latest stable version was 3.0.2. Note that I also imported the CM .Net SDK and System.Drawing.

Next I downloaded the latest english language data files and placed them into the required tessdata sub-folder. I also updated the properties of each so that they copy to the output folder if needed.

I decide to now implement the remove ocr rendition feature. One method will work on a single record and a second method will work on a set of tagged objects (same approach as with the Client Addin). To make it super simple I'm not presenting any sort of user interface or options.

#region Remove Ocr Rendition
public static bool RemoveOcrRendition(Record record)
{
    return record.RemoveOcrRendition();
}
public static void RemoveOcrRenditions(TrimMainObjectSearch forTaggedObjects)
{
    foreach (var result in forTaggedObjects)
    {
        HP.HPTRIM.SDK.Record record = result as HP.HPTRIM.SDK.Record;
        if ((HP.HPTRIM.SDK.Record)record != null)
        {
            RemoveOcrRendition(record);
        }
    }
} 
#endregion

I again used an extension method, this time naming it "RemoveOcrRendition". I create a new class named "RecordExtensions", mark it static, and implement the functionality. I also add one last extension method that handles the creation of a new ocr rendition. The contents of that class is included below.

using HP.HPTRIM.SDK;
namespace CMRamble.Ocr
{
    public static class RecordExtensions
    {
        public static void AddOcrRendition(this Record record, string fileName)
        {
            if (record.HasOcrRendition()) record.RemoveOcrRendition();
            record.ChildRenditions.NewRendition(fileName, RenditionType.Ocr, "Ocr");
        }
        public static bool RemoveOcrRendition(this Record record)
        {
            bool removed = false;
            for (uint i = 0; i < record.ChildRenditions.Count; i++)
            {
                RecordRendition rendition = record.ChildRenditions.getItem(i) as RecordRendition;
                if ((RecordRendition)rendition != null && rendition.TypeOfRendition == RenditionType.Ocr)
                {
                    rendition.Delete();
                    removed = true;
                }
            }
            record.Save();
            return removed;
        }
        public static bool HasOcrRendition(this Record record)
        {
            for (uint i = 0; i < record.ChildRenditions.Count; i++)
            {
                RecordRendition rendition = record.ChildRenditions.getItem(i) as RecordRendition;
                if ((RecordRendition)rendition != null && rendition.TypeOfRendition == RenditionType.Ocr)
                {
                    return true;
                }
            }
            return false;
        }
    }
}

Now that I have the remove ocr rendition functionality complete I can move onto the update functionality. In order to OCR the file I must first extract it to disk. Then I can extract the text by calling the tesseract library and saving the results back as a new ocr rendition. The code below implements this within the Record Controller class (which is invoked by the addin).

#region Update Ocr Rendition
public static bool UpdateOcrRendition(Record record)
{
    bool success = false;
    string extractedFilePath = string.Empty;
    string ocrFilePath = string.Empty;
    try
    {
        // get a temp working location on disk
        var rootDirectory = Path.Combine(Path.GetTempPath(), "cmramble_ocr");
        if (!Directory.Exists(rootDirectory)) Directory.CreateDirectory(rootDirectory);
        // formulate file name to extract, delete if exists for some reason
        extractedFilePath = Path.Combine(rootDirectory, $"{record.Uri}.{record.Extension}");
        ocrFilePath = Path.Combine(rootDirectory, $"{record.Uri}.txt");
        FileHelper.Delete(extractedFilePath);
        FileHelper.Delete(ocrFilePath);
        // fetch document
        record.GetDocument(extractedFilePath, false, "OCR", string.Empty);
        // get the OCR text
        ocrFilePath = TextExtractor.ExtractFromFile(extractedFilePath);
        // use record extension method that removes existing OCR rendition (if exists)
        record.AddOcrRendition(ocrFilePath);
        record.Save();
        success = true;
    }
    catch (Exception ex)
    {
    }
    finally
    {
        FileHelper.Delete(extractedFilePath);
        FileHelper.Delete(ocrFilePath);
    }
    return success;
}
public static void UpdateOcrRenditions(TrimMainObjectSearch forTaggedObjects)
{
    foreach (var result in forTaggedObjects)
    {
        HP.HPTRIM.SDK.Record record = result as HP.HPTRIM.SDK.Record;
        if ((HP.HPTRIM.SDK.Record)record != null)
        {
            UpdateOcrRendition(record);
        }
    }
}
#endregion

I placed all of the tesseract logic into a new class named TextExtractor. Within that class I have one method that takes a file name and returns the name of a file containing all of the ocr text. If I use tesseract on a PDF though it will give me back the text layers from within the PDF, which defeats my goal. I want tesseract to OCR the images within the PDF.

To accomplish that I used the Xpdf command line utility pdftopng, which extracts all of the images to disk. I then iterate over each image (just like I did within the original powershell script) to generate new OCR content. As each image is processed the results are appended to an ocr text file. That text file is what is returned to the record controller.

using CMRamble.Ocr.Util;
using System;
using System.Diagnostics;
using System.IO;
using System.Linq;
using Tesseract;
namespace CMRamble.Ocr
{
    public static class TextExtractor
    {
        /// <summary>
        /// Exports all images from PDF and then runs OCR over each image, returning the name of the file on disk holding the OCR results
        /// </summary>
        /// <param name="filePath">Source file to be OCR'd</param>
        /// <returns>Name of file containing OCR contents</returns>
        public static string ExtractFromFile(string filePath)
        {
            var ocrFileName = string.Empty;
            var extension = Path.GetExtension(filePath).ToLower();
            if (extension.Equals(".pdf"))
            {   
                // must break out the original images within the PDF and then OCR those
                var localDirectory = Path.Combine(Path.GetDirectoryName(filePath), Path.GetFileNameWithoutExtension(filePath));
                ocrFileName = Path.Combine(Path.GetDirectoryName(filePath), Path.GetFileNameWithoutExtension(filePath) + ".txt");
                FileHelper.Delete(ocrFileName);
                // call xpdf util pdftopng passing PDF and location to place images
                Process p = new Process();
                p.StartInfo.UseShellExecute = false;
                p.StartInfo.RedirectStandardOutput = true;
                p.StartInfo.FileName = "pdftopng";
                p.StartInfo.Arguments = $"\"{filePath}\" \"{localDirectory}\"";
                p.Start();
                string output = p.StandardOutput.ReadToEnd();
                p.WaitForExit();
                // find all the images that were extracted
                var images = Directory.GetFiles(Directory.GetParent(localDirectory).FullName, "*.png").ToList();
                foreach (var image in images)
                {
                    // spin up an OCR engine and have it dump text to the OCR text file
                    using (var engine = new TesseractEngine(@"./tessdata", "eng", EngineMode.Default))
                    {
                        using (var img = Pix.LoadFromFile(image))
                        {
                            using (var page = engine.Process(img))
                            {
                                File.AppendAllText(ocrFileName, page.GetText() + Environment.NewLine);
                            }
                        }
                    }
                    // clean-up as we go along
                    File.Delete(image);
                }
            }
            return ocrFileName;
        }
    }
}

All done! I can now compile the add-in and play with it. First I added the menu links to my home ribbon. As you can see below, clicking the remove ocr rendition link changes the number of renditions available.

Along the same line, if I click update ocr rendition then the number of renditions is increased...

In the next post I'll incorporate the same functionality within an event processor plugin, so that all records have their content OCR'd via tesseract.

You can download the full source for this solution here:

https://github.com/HPECM/Community/tree/master/CMRamble/Ocr