Many thanks again, but it seems I hit a snag just inches from the goal line...
I successfully removed my outdated version of Adobe Reader, installed Adobe Reader X, and set the preference flags as you instructed.
The snag came in the next step when I tried to run the OTL fix: the machine locked up again in much the same way that it did last week (in one of our first cleanup sessions).
The cursor's response to the mouse was the only sign of life, so I had to pull the plug to reboot.
Thinking I'd done something wrong, I tried again (after removing my trial version of Malwarebytes) but the machine locked up again while in the midst of shutting down.
Apparently no harm done -- I was simply unable to run the final OTL fix (and therefore did not run OTL clean-up, either).
So close and yet so far....