class Program
    {
        static void Main(string[] args)
        {
            AddCommentToPresentation("Sample.pptx",
            "Zeeshan", "MZ",
            "This is my programmatically added comment.");

        }
        // Adds a comment to the first slide of the presentation document.
        // The presentation document must contain at least one slide.
        private static void AddCommentToPresentation(string file, string initials, string name, string text)
        {
            using (PresentationDocument doc = PresentationDocument.Open(file, true))
            {

                // Declare a CommentAuthorsPart object.
                CommentAuthorsPart authorsPart;

                // Verify that there is an existing comment authors part. 
                if (doc.PresentationPart.CommentAuthorsPart == null)
                {
                    // If not, add a new one.
                    authorsPart = doc.PresentationPart.AddNewPart<CommentAuthorsPart>();
                }
                else
                {
                    authorsPart = doc.PresentationPart.CommentAuthorsPart;
                }

                // Verify that there is a comment author list in the comment authors part.
                if (authorsPart.CommentAuthorList == null)
                {
                    // If not, add a new one.
                    authorsPart.CommentAuthorList = new CommentAuthorList();
                }

                // Declare a new author ID.
                uint authorId = 0;
                CommentAuthor author = null;

                // If there are existing child elements in the comment authors list...
                if (authorsPart.CommentAuthorList.HasChildren)
                {
                    // Verify that the author passed in is on the list.
                    var authors = authorsPart.CommentAuthorList.Elements<CommentAuthor>().Where(a => a.Name == name && a.Initials == initials);

                    // If so...
                    if (authors.Any())
                    {
                        // Assign the new comment author the existing author ID.
                        author = authors.First();
                        authorId = author.Id;
                    }

                    // If not...
                    if (author == null)
                    {
                        // Assign the author passed in a new ID                        
                        authorId = authorsPart.CommentAuthorList.Elements<CommentAuthor>().Select(a => a.Id.Value).Max();
                    }
                }

                // If there are no existing child elements in the comment authors list.
                if (author == null)
                {

                    authorId++;

                    // Add a new child element(comment author) to the comment author list.
                    author = authorsPart.CommentAuthorList.AppendChild<CommentAuthor>
                        (new CommentAuthor()
                        {
                            Id = authorId,
                            Name = name,
                            Initials = initials,
                            ColorIndex = 0
                        });
                }

                // Get the first slide, using the GetFirstSlide method.
                SlidePart slidePart1 = GetFirstSlide(doc);

                // Declare a comments part.
                SlideCommentsPart commentsPart;

                // Verify that there is a comments part in the first slide part.
                if (slidePart1.GetPartsOfType<SlideCommentsPart>().Count() == 0)
                {
                    // If not, add a new comments part.
                    commentsPart = slidePart1.AddNewPart<SlideCommentsPart>();
                }
                else
                {
                    // Else, use the first comments part in the slide part.
                    commentsPart = slidePart1.GetPartsOfType<SlideCommentsPart>().First();
                }

                // If the comment list does not exist.
                if (commentsPart.CommentList == null)
                {
                    // Add a new comments list.
                    commentsPart.CommentList = new CommentList();
                }

                // Get the new comment ID.
                uint commentIdx = author.LastIndex == null ? 1 : author.LastIndex + 1;
                author.LastIndex = commentIdx;

                // Add a new comment.
                Comment comment = commentsPart.CommentList.AppendChild<Comment>(
                    new Comment()
                    {
                        AuthorId = authorId,
                        Index = commentIdx,
                        DateTime = DateTime.Now
                    });

                // Add the position child node to the comment element.
                comment.Append(
                    new Position() { X = 100, Y = 200 },
                    new Text() { Text = text });

                // Save the comment authors part.
                authorsPart.CommentAuthorList.Save();

                // Save the comments part.
                commentsPart.CommentList.Save();
            }
        }
        // Get the slide part of the first slide in the presentation document.
        private static SlidePart GetFirstSlide(PresentationDocument presentationDocument)
        {
            // Get relationship ID of the first slide
            PresentationPart part = presentationDocument.PresentationPart;
            SlideId slideId = part.Presentation.SlideIdList.GetFirstChild<SlideId>();
            string relId = slideId.RelationshipId;

            // Get the slide part by the relationship ID.
            SlidePart slidePart = (SlidePart)part.GetPartById(relId);

            return slidePart;
        }

    }

class Program
    {
        static void Main(string[] args)
        {

            using (PresentationEx pres = new PresentationEx())
            {
                //Adding Empty slide
                pres.Slides.AddEmptySlide(pres.LayoutSlides[0]);

                //Adding Autthor
                CommentAuthorEx author = pres.CommentAuthors.AddAuthor("Zeeshan", "MZ");

                //Position of comments

                PointF point = new PointF();
                point.X = 1;
                point.Y = 1;

                //Adding slide comment for an author on slide
                author.Comments.AddComment("Hello Zeeshan, this is slide comment", pres.Slides[0], point, DateTime.Now);
                pres.Write("Comments.pptx");
            }
        }
    }