In recent weeks, Reader has been giving "failed to update" messages, but was still working. But in a mad moment, I thought this should be fixed.
The advice from the Reader help page was to uninstall Reader, then run Adobe AcroCleaner.
Windows Uninstall didn't work. So today I used IOBit to uninstall Reader, ran AcroCleaner and installed Acrobat.
However after this, I checked what was on my C: drive by scanning for references to Acrobat. There is a vast amount of Acrobat clutter dating from 2019 to today's installation files. No wonder the program was confused. Surely any update should delete any obsolete files? Which of these can be removed without harm to the present installation?