How to Insert Comment into Word Document using C#. More details and steps can be found here https://kb.aspose.com/words/net/how-to-insert-comment-into-word-document-using-c-sharp/

How to Insert Comment into Word Document using C#.cs

using Aspose.Words;
using System;

namespace InsertCommentinWord
{
    class how_to_insert_comment_into_word_document_using_c_sharp
    {
        public static void InsertComment(String directorypath)
        {
            //Set Aspose license before importing document. 
            Aspose.Words.License AsposeWordsLicense = new Aspose.Words.License();
            AsposeWordsLicense.SetLicense(directorypath + @"Aspose.Words.lic");

            //Import the Document into Aspose.Words DOM. 
            Document doc = new Document(directorypath + "input.docx");
            DocumentBuilder builder = new DocumentBuilder(doc);

            //Move the cursor to the beginning of the document. 
            builder.MoveToDocumentStart();
            //Insert comment to first paragraph of document.
            Comment comment = new Comment(doc, "Aspose.Words", "AW", DateTime.Today);
            builder.CurrentParagraph.AppendChild(comment);
            comment.Paragraphs.Add(new Paragraph(doc));
            comment.FirstParagraph.Runs.Add(new Run(doc, "Comment text."));

            //Save the Document
            doc.Save(directorypath + @"output.docx", SaveFormat.Docx);
        }
    }
}