private static void ExecutedPasteRoutedCommand(object sender, ExecutedRoutedEventArgs e)
        {
            RichTextBoxEx richTextBoxEx = sender as RichTextBoxEx;

            if (richTextBoxEx != null && !richTextBoxEx.IsReadOnly)
            {
                if (richTextBoxEx.IsReadOnlyWithNavigation)
                {
                    return;
                }
                richTextBoxEx.Paste();
            }
        }