Downloads won't open unless renamed

Callum Kaye wrote:

This is an odd one. When I download a file in Safari, I'm told:

The file "X" couldn't be opened because you don't have permission to view it. To view or change permissions, select the item in the Finder and choose File > Get info

As far as I know, I haven't changed settings and I'm the only user. Oddly, if I go into the Downloads folder, find the file and change the filename, I can open it. Any ideas?

This is all files downloaded or just your file" X"...(?) What is file "X"?

To trouble shoot further you can:

—Test issue in another user (or guest user) account Change Users & Groups settings on Mac - Apple Support

This will tell you if it a universal issue or isolated to your user/admin account. 

—A SafeBoot How to use safe mode on your Mac - Apple Support will sort many anomalies

Login and test. Reboot as normal and test.

This test will tell you if third party interference; most* extensions etc are not loaded in safe boot mode.