Leo, thanks for the suggestions. Going back to 365 did not fix the issue. I uninstalled all versions. I then tried to install MSO 2016 Pro again (the version on my older machine) but this time, with 365 uninstalled, it would not activate this time (it did not ask when 365 was also installed). I logged into the MS account for the new machine (it is under another person's name) and it showed the new MSO 2016 available to download and the activation key! These were not there before MSO365 had been activated. Happy ending: I have installation "media" - an ISO file - an activation key and a working installation of MSO 2016 on the new machine. Viewer in DOpus work. Whew!