/// <summary>
            /// Updates document comments of Doc file  
            /// </summary> 
            public static void UpdateComments()
            {
                try
                {
                    //ExStart:UpdateDocumentComment
                    // initialize DocFormat
                    DocFormat docFormat = new DocFormat(Common.MapSourceFilePath(filePath));

                    // extract comments
                    DocComment[] comments = docFormat.ExtractComments();

                    if (comments.Length > 0)
                    {
                        // get first comment if exist
                        var comment = comments[0];

                        // change comment's author
                        comment.Author = "Jack London";

                        // change comment's text
                        comment.Text = "This comment is created using GroupDocs.Metadata";

                        // update comment
                        docFormat.UpdateComment(comment.Id, comment);
                    }

                    // save file in destination folder
                    docFormat.Save(Common.MapDestinationFilePath(filePath));

                    Console.WriteLine("File saved in destination folder.");
                    //ExEnd:UpdateDocumentComment

                }
                catch (Exception exp)
                {
                    Console.WriteLine(exp.Message);
                }
            }