Can't open Pages docs

Running OS 10.15.1 Catalina, Pages 8.2 on iMac. Upgraded recently but this problem was not evident until today. Can't open existing Pages docs stored either on internal drive or iCloud.

I have been able to open some of the documents on iCloud by logging into my account, but in browser. Would have to paste / retype / reformat the documents all over again in Pages, a nightmare.

Anyone has any idea how to overcome this?