Hello spiriou,
I understand you're having some trouble sending new documents through pages. Hopefully I can provide some helpful resources.
Add your Desktop and Documents files to iCloud Drive
Steps 1-3 are to ensure your Mac is up to date on macOS, make sure you're signed into iCloud and to get iCloud set up on all your other devices. Next you want to make sure System Preferences > Apple ID > iCloud > iCloud Drive is enabled. Next to iCloud Drive, click options, and then make sure 'Desktop and Documents Folders' is enabled.
If these conditions are met and you are still having iCloud Drive access issues, Contact Apple Support.
This may be helpful for creating a backup - Back up your Mac with Time Machine
Thanks for reaching out to Apple Support Communities.