When the computer wakes up after an overnight rest (was it sleeping or hibernating, and what is the difference?) Adobe Acrobat is open and displayed on top of it is a window which says:

"Acrobat Reader
There was an error opening this document. This file cannot be found."

It's 2015 Release Version 2015.007.20033, if that's relevant.

This happens only after I have been absent for many hours. It doesn't happen after a normal, i.e. short, absence during which the display is switched off.

What can be causing this?