I have solved my problem but thanks for the suggestion.
I have recently upgraded to Windows 10.
The original issue appears to relate to a particular file and not the Adobe Acrobat Reader itself so I should have left it alone in the first place. When reinstalling Adobe Acrobat, the key was not to click on the downloaded file at the bottom left of the screen but to go to Downloads in File Explorer where you need to click on the tools at the top of the screen and run the installation as the Administrator.