I have a .pages file I've worked on as recently as May. When I tried to open it the Console.app reported:
9/2/16 7:21:44.392 PM CoreServicesUIAgent: Error -60005 creating authorization
The file didn't open. I created a new document and save it, and was able to reopen it; though Pages DID throw the same error (but the file window opened).
I deleted and re-downloaded Pages from the App store. Preview.app confirms the app has readable content.
I have done first aid on the disk, and am on El Cap 10.11.6.
Pages is up to date, 5.6.2.