bookmark

      object oRngoBookMarkStart = 12;
            object oRngoBookMarkEnd = 34;      
            Microsoft.Office.Interop.Word.Range rngBKMarkSelection = doc.Range(ref oRngoBookMarkStart, ref oRngoBookMarkEnd);
            rngBKMarkSelection.Text = DateTime.Now.ToShortDateString();
            rngBKMarkSelection.Font.Bold = 1;
            rngBKMarkSelection.Font.Color = Microsoft.Office.Interop.Word.WdColor.wdColorBlue;
            object oRng = rngBKMarkSelection;
            doc.Bookmarks.Add("LetterDate", ref oRng);