While converting DOC to PDF bot is stopped in try block and pop open

I have one issue :

While converting DOC to PDF bot is stopped in try block and pop open and showing message

Word will now convert your PDF to an editable Word document. This may take a while. The resulting Word document will be optimized to allow you to edit the text, so it might not look exactly like the original PDF, especially if the original file contained lots of graphics.

i want bot should throw exception and process catch block. but bot is not throwing exception.