using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using DocumentFormat.OpenXml.Packaging;
using DocumentFormat.OpenXml.Wordprocessing;
namespace OpenXML_SDK
{
    class Program
    {
        static void Main(string[] args)
        {
            AddCommentOnFirstParagraph("Insert a Comment in Word Processing document.docx",
            "author", "initials", "This is my comment.");
        }
        // Insert a comment on the first paragraph.
        public static void AddCommentOnFirstParagraph(string fileName,
            string author, string initials, string comment)
        {
            // Use the file name and path passed in as an 
            // argument to open an existing Wordprocessing document. 
            using (WordprocessingDocument document =
                WordprocessingDocument.Open(fileName, true))
            {
                // Locate the first paragraph in the document.
                Paragraph firstParagraph =
                    document.MainDocumentPart.Document.Descendants<Paragraph>().First();
                Comments comments = null;
                string id = "0";

                // Verify that the document contains a 
                // WordProcessingCommentsPart part; if not, add a new one.
                if (document.MainDocumentPart.GetPartsCountOfType<WordprocessingCommentsPart>() > 0)
                {
                    comments =
                        document.MainDocumentPart.WordprocessingCommentsPart.Comments;
                    if (comments.HasChildren)
                    {
                        // Obtain an unused ID.
                        id = comments.Descendants<Comment>().Select(e => e.Id.Value).Max();
                    }
                }
                else
                {
                    // No WordprocessingCommentsPart part exists, so add one to the package.
                    WordprocessingCommentsPart commentPart =
                        document.MainDocumentPart.AddNewPart<WordprocessingCommentsPart>();
                    commentPart.Comments = new Comments();
                    comments = commentPart.Comments;
                }

                // Compose a new Comment and add it to the Comments part.
                Paragraph p = new Paragraph(new Run(new Text(comment)));
                Comment cmt =
                    new Comment()
                    {
                        Id = id,
                        Author = author,
                        Initials = initials,
                        Date = DateTime.Now
                    };
                cmt.AppendChild(p);
                comments.AppendChild(cmt);
                comments.Save();

                // Specify the text range for the Comment. 
                // Insert the new CommentRangeStart before the first run of paragraph.
                firstParagraph.InsertBefore(new CommentRangeStart() { Id = id }, firstParagraph.GetFirstChild<Run>());

                // Insert the new CommentRangeEnd after last run of paragraph.
                var cmtEnd = firstParagraph.InsertAfter(new CommentRangeEnd() { Id = id }, firstParagraph.Elements<Run>().Last());

                // Compose a run with CommentReference and insert it.
                firstParagraph.InsertAfter(new Run(new CommentReference() { Id = id }), cmtEnd);
            }
        }
    }

}

using Aspose.Words;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Aspose_Word
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create an empty document and DocumentBuilder object.
            Document doc = new Document();
            DocumentBuilder builder = new DocumentBuilder(doc);

            // Create a Comment.
            Comment comment = new Comment(doc);
            // Insert some text into the comment.
            Paragraph commentParagraph = new Paragraph(doc);
            commentParagraph.AppendChild(new Run(doc, "This is comment!!!"));
            comment.AppendChild(commentParagraph);

            // Create CommentRangeStart and CommentRangeEnd.
            int commentId = 0;
            CommentRangeStart start = new CommentRangeStart(doc, commentId);
            CommentRangeEnd end = new CommentRangeEnd(doc, commentId);

            // Insert some text into the document.
            builder.Write("This is text before comment ");
            // Insert comment and comment range start.
            builder.InsertNode(comment);
            builder.InsertNode(start);
            // Insert some more text.
            builder.Write("This is commented text ");
            // Insert end of comment range.
            builder.InsertNode(end);
            // And finaly insert some more text.
            builder.Write("This is text aftr comment");

            // Save output document.
            doc.Save("Insert a Comment in Word Processing document.docx");
        }
    }
}