Outlook hangs after DC opens PDF

I have a user who is trying to open PDF attachments in Outlook 365. PDF attachments will open a window and the document or image actually appears, but after about 10-15 seconds, Reader DC displays "Not Responding" at the top of the window, and Outlook hangs. To gain control of Outlook again, one has to exit Outlook and restart the app.

I've tried going to Acrobat Reader DC and unclicking "Show onlin estorage when opening files", "Show online storage when saving files", and Show me messages when I loaunch Acrobat Reader", and the problem remains. I tried doing a repair install and also a full uninstall/reinstall of Acrobat Reader DC and this did  not solve the problem. 

The user can save the PDF attachments and then open them  from File Manager, but it would be a lot  more efficient to be able to open the PDF attachments form inside Outlook. 

Has anyone seen this happen and know of a fix?