I would not have guessed the two file formats to be compatible by simply changing the file extension. Will have to try that sometime.
If you want to go the other way and convert to PDF then you can always download the Cute PDF writer. Its a free app and it converts pretty much any file format to PDF. It installs as a virtual printer. Just open the file you want to convert, select print, choose the Cute PDF Writer printer then name the file whatever you want and it converts and saves the file in PDF format. Works great.