Hi John,
It looks like I won’t be able to install Wordfast on the subscription version of Word anyway, so I’ll take up your suggestion to try Felix. Apparently, MS blocked a lot of third-party tools built on Word when they moved to the subscription form.
However, I’m not super excited about CAT tools in general; my experience with the ones I've tried is that they don’t really help very much with my kind of work, compared with just using a good old word processor.
Jon Johanning