There’s a script-based solution here that does it via button presses; but if it came to that and I it was available, I’d be using Keyboard Maestro to do the controlling instead.
I tried using the save option in PDFpenPro’s AppleScript dictionary to see if I could save as Word (there’s no export option listed). But, I couldn’t find any list of the type options anywhere (I tried a few educated guesses around Word and DOCX variations), and as soon as I tried any file name variations, PDFpenPro would return a permission or a location based error code regardless when trying the save; I even fixed my disk permissions just in case it was something external fouling things up.
Just in case you hadn’t considered it, Don Kolafa’s approach on this thread might be worth considering.
But, supporting adding DOCX and not supporting adding PDF as a reference - how is that a thing any developer could consider as being a good approach?