Just found an answer here:
https://forum.pdf-xchange.com/ ... 41&t=11323
Will try that first. (Apologies, I thought I did a thorough search prior to posting)

All good re-installing fixed the problem

Hi! I recently installed the trial version of PDF-XChange, after evaluating and deciding to purchase, I added in the license key via PDF Xchange --> preferences -->about--> and entered serial key. I believe I have PDF-XChange PRO Version: 5.0.262 and MS office 2010. When I use the Add-in in Word to ...