Even though this is the WPF forum, I have encountered the same problem in a WinForms application. The error I am getting is that "Value of type 'RadDocument' cannot be converted to 'RadDocument'. I have attached an image with the code and error.
I tried using the code directly from this page ("http://www.telerik.com/help/winforms/richtexteditor-import-export.html") and simplified it to try to eliminate the error. No luck. Any suggestions?