PM> Install-Package Spire.Doc

using Spire.Doc;
using Spire.Doc.Documents;
using Spire.Doc.Fields;

namespace AddComments
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //Initialize an instance of the Document class
            Document document = new Document();
            //Load a Word document
            document.LoadFromFile(@"Sample.docx");

            //Get the first section in the document
            Section section = document.Sections[0];

            //Get the first paragraph in the section
            Paragraph paragraph = section.Paragraphs[0];
            //Add a comment to the paragraph
            Comment comment = paragraph.AppendComment("This comment is added using Spire.Doc for .NET.");
            //Set comment author
            comment.Format.Author = "Eiceblue";
            comment.Format.Initial = "CM";

            //Save the result document
            document.SaveToFile("AddCommentToParagraph.docx", FileFormat.Docx2013);
            document.Close();
        }
    }
}

Imports Spire.Doc
Imports Spire.Doc.Documents
Imports Spire.Doc.Fields

Namespace AddComments
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Initialize an instance of the Document class
            Dim document As Document = New Document()
            'Load a Word document
            document.LoadFromFile("Sample.docx")

            'Get the first section in the document
            Dim section As Section = document.Sections(0)

            'Get the first paragraph in the section
            Dim paragraph As Paragraph = section.Paragraphs(0)
            'Add a comment to the paragraph
            Dim comment As Comment = paragraph.AppendComment("This comment is added using Spire.Doc for .NET.")
            'Set comment author
            comment.Format.Author = "Eiceblue"
            comment.Format.Initial = "CM"

            'Save the result document
            document.SaveToFile("AddCommentToParagraph.docx", FileFormat.Docx2013)
            document.Close()
        End Sub
    End Class
End Namespace

using Spire.Doc;
using Spire.Doc.Documents;
using Spire.Doc.Fields;

namespace AddCommentsToText
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //Initialize an instance of the Document class
            Document document = new Document();
            //Load a Word document
            document.LoadFromFile(@"CommentTemplate.docx");

            //Find a specific string
            TextSelection find = document.FindString("Microsoft Office", false, true);

            //Create the comment start mark and comment end mark
            CommentMark commentmarkStart = new CommentMark(document);
            commentmarkStart.Type = CommentMarkType.CommentStart;
            CommentMark commentmarkEnd = new CommentMark(document);
            commentmarkEnd.Type = CommentMarkType.CommentEnd;

            //Create a comment and set its content and author
            Comment comment = new Comment(document);
            comment.Body.AddParagraph().Text = "Developed by Microsoft.";
            comment.Format.Author = "Shaun";

            //Get the found text as a single text range
            TextRange range = find.GetAsOneRange();

            //Get the owner paragraph of the text range
            Paragraph para = range.OwnerParagraph;

            //Add the comment to the paragraph
            para.ChildObjects.Add(comment);

            //Get the index of text range in the paragraph
            int index = para.ChildObjects.IndexOf(range);

            //Set comment ID for the comment mark start and comment mark end
            commentmarkStart.CommentId = comment.Format.CommentId;
            commentmarkEnd.CommentId = comment.Format.CommentId;

            //Insert the comment start mark before the text range
            para.ChildObjects.Insert(index, commentmarkStart);
            //Insert the comment end mark after the text range
            para.ChildObjects.Insert(index + 2, commentmarkEnd);

            //Save the result document
            document.SaveToFile("AddCommentForText.docx", FileFormat.Docx2013);
            document.Close();
        }
    }
}

Imports Spire.Doc
Imports Spire.Doc.Documents
Imports Spire.Doc.Fields

Namespace AddCommentsToText
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Initialize an instance of the Document class
            Dim document As Document = New Document()
            'Load a Word document
            document.LoadFromFile("CommentTemplate.docx")

            'Find a specific string
            Dim find As TextSelection = document.FindString("Microsoft Office", False, True)

            'Create the comment start mark and comment end mark
            Dim commentmarkStart As CommentMark = New CommentMark(document)
            commentmarkStart.Type = CommentMarkType.CommentStart
            Dim commentmarkEnd As CommentMark = New CommentMark(document)
            commentmarkEnd.Type = CommentMarkType.CommentEnd

            'Create a comment and set its content and author
            Dim comment As Comment = New Comment(document)
            comment.Body.AddParagraph().Text = "Developed by Microsoft."
            comment.Format.Author = "Shaun"

            'Get the found text as a single text range
            Dim range As TextRange = find.GetAsOneRange()

            'Get the owner paragraph of the text range
            Dim para As Paragraph = range.OwnerParagraph

            'Add the comment to the paragraph
            para.ChildObjects.Add(comment)

            'Get the index of text range in the paragraph
            Dim index As Integer = para.ChildObjects.IndexOf(range)

            'Insert the comment start mark before the text range
            para.ChildObjects.Insert(index, commentmarkStart)
            'Insert the comment end mark after the text range
            para.ChildObjects.Insert(index + 2, commentmarkEnd)

            'Save the result document
            document.SaveToFile("AddCommentForText.docx", FileFormat.Docx2013)
            document.Close()
        End Sub
    End Class
End Namespace

using Spire.Doc;
using Spire.Doc.Fields;

namespace ReplyToComments
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //Initialize an instance of the Document class
            Document document = new Document();
            //Load a Word document
            document.LoadFromFile(@"AddCommentToParagraph.docx");

            //Get the first comment in the document
            Comment comment1 = document.Comments[0];

            //Create a new comment and specify its author and content
            Comment replyComment1 = new Comment(document);
            replyComment1.Format.Author = "Michael";
            replyComment1.Body.AddParagraph().AppendText("Spire.Doc is a wonderful Word library.");

            //Add the comment as a reply to the first comment
            comment1.ReplyToComment(replyComment1);

            //Save the result document
            document.SaveToFile("ReplyToComment.docx", FileFormat.Docx2013);
            document.Close();
        }
    }
}

Imports Spire.Doc
Imports Spire.Doc.Fields

Namespace ReplyToComments
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Initialize an instance of the Document class
            Dim document As Document = New Document()
            'Load a Word document
            document.LoadFromFile("AddCommentToParagraph.docx")

            'Get the first comment in the document
            Dim comment1 As Comment = document.Comments(0)

            'Create a new comment and specify its author and content
            Dim replyComment1 As Comment = New Comment(document)
            replyComment1.Format.Author = "Michael"
            replyComment1.Body.AddParagraph().AppendText("Spire.Doc is a wonderful Word library.")

            'Add the comment as a reply to the first comment
            comment1.ReplyToComment(replyComment1)

            'Save the result document
            document.SaveToFile("ReplyToComment.docx", FileFormat.Docx2013)
            document.Close()
        End Sub
    End Class
End Namespace

using Spire.Doc;

namespace DeleteComments
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //Initialize an instance of the Document class
            Document document = new Document();
            //Load a Word document
            document.LoadFromFile(@"AddCommentToParagraph.docx");

            //Delete the first comment in the document
            document.Comments.RemoveAt(0);

            //Delete all comments in the document
            //document.Comments.Clear();

            //Save the result document
            document.SaveToFile("DeleteComment.docx", FileFormat.Docx2013);
            document.Close();
        }
    }
}

Imports Spire.Doc

Namespace DeleteComments
    Friend Class Program
        Private Shared Sub Main(ByVal args As String())
            'Initialize an instance of the Document class
            Dim document As Document = New Document()
            'Load a Word document
            document.LoadFromFile("AddCommentToParagraph.docx")

            'Delete the first comment in the document
            document.Comments.RemoveAt(0)

            'Delete all comments in the document
            'document.Comments.Clear();

            'Save the result document
            document.SaveToFile("DeleteComment.docx", FileFormat.Docx2013)
            document.Close()
        End Sub
    End Class
End Namespace