Merging Word Documents in Dynamics 365 Using Only Built-In Features

 Below is a straightforward approach to merge two Word documents in Dynamics 365—without resorting to third-party paid connectors or extensions. By leveraging a custom Action, a Power Automate flow, and a plugin with OpenXML (embedded via ILRepack), you can seamlessly combine Word files and store the merged result, all in one out-of-the-box solution.

1. Create a Custom Action in Dynamics 365

• In your D365 solution, add a new Action (e.g., new_mergeaction).
• Define two input parameters as string fields, Document1 and Document2.
• Define one output parameter as a string field, MergedDocument.
• This Action will be called by the plugin to perform the merge.

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2. Create a Power Automate Flow

1. Add Get file content (SharePoint) actions to retrieve both Word documents.
2. Insert a Perform an unbound/bound action step (Dataverse connector) targeting the Action from step 1:
   • Map Document1 to @{body('Get_file_content_1')}.
       for example:  outputs('Get_file_content')?['body']['$content']
   • Map Document2 to @{body('Get_file_content_2')}.
     
     
3. The Action responds with MergedDocument (base64).

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3. Develop the Plugin and Register It on the Action

Use a plugin that:

• Accepts Document1 and Document2 from InputParameters.
• Converts them from base64 (or parses "$content" if full JSON).
• Merges the docs via OpenXML, adding a page break in between.
• Returns base64 in MergedDocument.

Below is a simplified example (text representation):

using System;

using System.IO;

using DocumentFormat.OpenXml.Packaging;

using DocumentFormat.OpenXml.Wordprocessing;

using Microsoft.Xrm.Sdk;

using Newtonsoft.Json.Linq;

namespace WordDocumentsMerge

{

    public class Merge : IPlugin

    {

        public void Execute(IServiceProvider serviceProvider)

        {

            var context = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));

            if (!context.InputParameters.Contains("Document1") || !context.InputParameters.Contains("Document2"))

            {

                throw new InvalidPluginExecutionException("Missing docs");

            }

            string doc1Raw = context.InputParameters["Document1"].ToString();

            string doc2Raw = context.InputParameters["Document2"].ToString();

            string doc1Json = NormalizeInput(doc1Raw);

            string doc2Json = NormalizeInput(doc2Raw);

            string base64Doc1 = ExtractBase64IfJson(doc1Json);

            string base64Doc2 = ExtractBase64IfJson(doc2Json);

            byte[] doc1Bytes = Convert.FromBase64String(base64Doc1);

            byte[] doc2Bytes = Convert.FromBase64String(base64Doc2);

            byte[] mergedBytes = MergeDocs(doc1Bytes, doc2Bytes);

            context.OutputParameters["MergedDocument"] = Convert.ToBase64String(mergedBytes);

        }

        private string NormalizeInput(string input)

        {

            input = input.Trim();

            if (input.StartsWith("\"") && input.EndsWith("\""))

            {

                input = input.Substring(1, input.Length - 2);

                input = input.Replace("\\\"", "\"");

            }

            return input;

        }

        private string ExtractBase64IfJson(string input)

        {

            if (!input.StartsWith("{"))

            {

                return input;

            }

            JObject obj = JObject.Parse(input);

            var content = (string)obj["$content"];

            if (string.IsNullOrEmpty(content))

            {

                throw new InvalidPluginExecutionException("No '$content' found.");

            }

            return content;

        }

        private byte[] MergeDocs(byte[] file1, byte[] file2)

        {

            using (var ms = new MemoryStream())

            {

                ms.Write(file1, 0, file1.Length);

                ms.Position = 0;

                using (var mainDoc = WordprocessingDocument.Open(ms, true))

                {

                    var body = mainDoc.MainDocumentPart.Document.Body;

                    // Insert a page break before appending the second doc

                    var pageBreak = new Paragraph(

                        new Run(

                            new Break { Type = BreakValues.Page }

                        )

                    );

                    body.Append(pageBreak);

                    var altId = "AltChunkId";

                    var altPart = mainDoc.MainDocumentPart.AddAlternativeFormatImportPart(

                        AlternativeFormatImportPartType.WordprocessingML, altId);

                    using (var ms2 = new MemoryStream(file2))

                    {

                        altPart.FeedData(ms2);

                    }

                    body.Append(new AltChunk { Id = altId });

                    mainDoc.MainDocumentPart.Document.Save();

                }

                return ms.ToArray();

            }

        }

    }

}

The key merging logic:

1. Open the first doc in a MemoryStream (expandable).
2. Insert a page break.
3. Use AltChunk to append the second doc.
4. Save and return base64.

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4. Merge OpenXML with Your Plugin via ILRepack

Because D365 runs plugins in a sandbox, external references like OpenXML must be embedded in your assembly. Use a command like:

"C:\WHSC\packages\ILRepack.2.0.36\tools\ILRepack.exe" /out:C:\WHSC\WordDocumentsMerge\bin\Debug\Merge.dll /keyfile:C:\WHSC\WordDocumentsMerge\WordDocumentsMerge.snk C:\WHSC\WordDocumentsMerge\bin\Debug\WordDocumentsMerge.dll C:\WHSC\WordDocumentsMerge\bin\Debug\DocumentFormat.OpenXml.dll

Then register Merge.dll in the Plugin Registration Tool on your custom Action.

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5. Receive and Store the Merged File in Power Automate

• The Action call returns MergedDocument in base64.
• Add a Create file step (SharePoint) to store the final Word file

Conclusion
With these steps, you can merge two Word documents entirely through standard Microsoft-provided features in Dynamics 365 and Power Automate—no extra costs or third-party extensions required. The combination of a custom Action, a plugin merged with OpenXML, and ILRepack ensures a secure, sandbox-compatible solution that leverages only out-of-the-box functionality.