Hi @Muruga Nandan, the error you're encountering is related to how you're adding the DocumentSettingsPart to the document.

Can you please change AddNewPart() to AddNewPart<DocumentSettingsPart>() to properly specify the type. 

Thank you.

Hi @Muruga Nandan 

The method AddNewPart() requires T to be a class derived from OpenXmlPart and also have a public parameterless constructor.This works in older versions of the DocumentFormat.OpenXml library (e.g., v2.5 and earlier). But in later versions (like v2.11+), DocumentSettingsPart no longer has a public parameterless constructor, or the generics constraints are different.

replace
settingsPart = document.MainDocumentPart.AddNewPart();

with

settingsPart = document.MainDocumentPart.AddNewPart("application/vnd.openxmlformats-officedocument.wordprocessingml.settings+xml", "settings");

Can you please try with the below code.

using System;

using System.IO;

using DocumentFormat.OpenXml.Packaging;

using DocumentFormat.OpenXml.Wordprocessing;

namespace OutSystems.NssOpenXML_Enable_Track_Changes

{

    public class CssOpenXML_Enable_Track_Changes : IssOpenXML_Enable_Track_Changes

    {

        public void MssAction_OpenXML_Enable_Track_Changes(string ssInp_Base64, out string ssProcessed_Base64)

        {

            // Initialize output

            ssProcessed_Base64 = string.Empty;

            try

            {

                // Decode the base64 string to a byte array

                byte[] inputBytes = Convert.FromBase64String(ssInp_Base64);

                using (MemoryStream inputStream = new MemoryStream(inputBytes))

                using (MemoryStream outputStream = new MemoryStream())

                {

                    // Open the WordprocessingDocument

                    using (WordprocessingDocument document = WordprocessingDocument.Open(inputStream, true))

                    {

                        // Get or create the document settings part (corrected)

                        DocumentSettingsPart settingsPart = document.MainDocumentPart.DocumentSettingsPart;

                        if (settingsPart == null)

                        {

                            // Correct way to add a new DocumentSettingsPart

                            settingsPart = document.MainDocumentPart.AddNewPart();

                            settingsPart.Settings = new Settings();

                        }

                        // Enable track changes

                        if (settingsPart.Settings == null)

                        {

                            settingsPart.Settings = new Settings();

                        }

                        // Remove existing TrackRevisions if any

                        var existingTrackRevisions = settingsPart.Settings.Elements().FirstOrDefault();

                        if (existingTrackRevisions != null)

                        {

                            existingTrackRevisions.Remove();

                        }

                        // Add new TrackRevisions

                        settingsPart.Settings.AppendChild(new TrackRevisions() { Val = OnOffValue.FromBoolean(true) });

                        // Save changes

                        settingsPart.Settings.Save();

                        document.MainDocumentPart.Document.Save();

                    }

                    // Reset stream position and copy to output

                    inputStream.Position = 0;

                    inputStream.CopyTo(outputStream);

                    // Convert to base64

                    ssProcessed_Base64 = Convert.ToBase64String(outputStream.ToArray());

                }

            }

            catch (Exception ex)

            {

                // Handle exceptions appropriately

                throw new Exception($"Error enabling track changes: {ex.Message}");

            }

        }

    }

}