Well despite numerous emails back & forth the best I can get from the (ahem) 'support team' is them telling me to check that my version of Acrobat Reader DC is up-to-date. This was from the team manager and came after I had told them I had gone as far as uninstalling & reinstalling, just to prove that it was.
My blood pressure is fine but life is too short, so I've uninstalled DC and installed Foxit instead, which works fine should anyone else encounter the same problem & need a quick solution that actually works!
