Sometimes it is necessary on a remote desktop server to disable the Adobe Reader Protected mode. On certain systems Adobe reader crashes when you try and open or close a PDF document. You can also get the "Access is denied" error when opening a PDF file from within Outlook.
The following needs to be done per user
To disable Protected Mode, open Acrobat Reader DC
Select "Edit" and "Preferences" from the menu
Select the "Security (Enhanced)" tab from the left panel
Untick "Enable Protected Mode at startup"
Scroll down to the bottom of that page and press "OK"