как ни пытаюсь, не могу текст с форматированием скопировать в RichTextBox, помогите, пожалуйста

 Application application = new Application();
            object File = "D:\\DOCs\\test.docx"; //this is the path
            object nullobject = System.Reflection.Missing.Value;
            application.DisplayAlerts = Microsoft.Office.Interop.Word.WdAlertLevel.wdAlertsNone; 
            Microsoft.Office.Interop.Word._Document docs =
            application.Documents.Open(ref File, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject, ref nullobject); 
            docs.ActiveWindow.Selection.WholeStory();
            docs.ActiveWindow.Selection.Copy();
            //Clipboard.SetText(docs.ActiveWindow.Selection.Text, TextDataFormat.Rtf);

            //rtfMain.Paste();

            rtfMain.AppendText(Clipboard.GetText(TextDataFormat.Rtf));

            //rtfMain.Document.Blocks.Clear();
            //rtfMain.Document.Blocks.Add(new Paragraph(new Run(Clipboard.GetText(TextDataFormat.Rtf))));

            docs.Close(ref nullobject, ref nullobject, ref nullobject);
            application.Quit(ref nullobject, ref nullobject, ref nullobject);