> I maintain four different operation manuals and occasionally work on more
> than one of them at a time. Is there a way to increase the number of recent
> files shown at the bottom of the Files drop-down menu?
Have you considered adding the files to a new book file? You can open
one or multiple selected files from a book window.
Another option is to create a folder of shortcuts for these files and
place it on the desktop or wherever it's most convenient to find, then
open the file(s) with the shortcut(s).