The recommended c# .net code to replace a bookmark with text appears very straight forward and I have seen the same code all over the net on so many websites (including your
Instead of altering the range directly, try something like:
Bookmark bookmark = doc.Bookmarks.get_Item(ref name); //Select the text. bookmark.Select(); //Overwrite the selection. wordApp.Selection.TypeText(text);
E.g. use your Word application instance to alter the document instead.