Is the user — by any chance — trying to open a PDF document from a shared drive? Is it throwing up an error message? This post will help you. This one is a sly little beggar. It’s Adobe’s default attempt to keep nasty things at bay — but it’s annoying.

Example: “I’ve got some documents on the T drive that won’t open.”

Resolution: Open Adobe Reader and go to Edit > Preferences > General. Un-tick the box at the bottom which says “Enable Protected Mode at startup”. There. All done.