Adobe DC on win10 - Once Adobe is open, opening any additional pdf does nothing

Hi Guys, hope you can help.

I have a user with a win10 machine and freshly installed copy of Adobe Acrobat Reader DC.

If you open a pdf, Adobe will open to display it. But once Acrobat is open, clicking on any additional PDFs either in WinExplorer, Outlook etc will result in nothing happening, if you then close Acrobat, and retry opening the new document, it will open, and the issue recurrs.

Tried uninstalling/reinstalling and checking the default associations.