Hi Peter Deep1,
Thanks for coming to Apple Support Communities for help with iCloud Drive. It sounds like you aren't able to save or edit some documents stored there.
Be sure and check out the iCloud Drive FAQ: iCloud Drive FAQ.
Have you checked on iCloud.com to see if files could be opened normally there?
Is Pages completely updated?
Have you tried signing out then back into iCloud in System Preferences > iCloud?
Check out this page too: Add your Desktop and Documents files to iCloud Drive and scroll to "Turn off Desktop and Documents". You may want to try moving the files out of iCloud, see if editing works and then re-save them.
"If you turn off iCloud Drive or sign out of iCloud, you have the option to keep a local copy of your files that are in iCloud Drive. Whether you decide to keep a local copy or not, a new Desktop and Documents folder is created in your home folder. If you choose to keep a local copy, your files in iCloud Drive are copied to a folder called iCloud Drive (Archive) in your home folder. Then you have the option to move any files that were in your iCloud Desktop and Documents, back to your new local Desktop and Documents."
If this doesn't resolve the issue, please contact Apple Support.
Have a fantastic day!