PDF files not opening with double-click

Mac OSX 10.11.6/Acrobat 10.1.1.

Suddenly pdf files won't open with a double click, I now have to open Acrobat and file>open.

Also, once they're open, they won't close by clicking the red close dot, I now have to go to file>close.

Please do not suggest changing the Open With default in the file info - they are all already set to default to Acrobat.

So frustrating!