After changing of the date of the file, the “pages” cannot read it

You should be running iOS 16.5 and Pages v13. If not, perform the respective updates, and then reassess if the issue you are experiencing remains.

And what do you mean by "After changing of the date of the file, the “pages” cannot read it?"

One thing you can try is to update your iOS to the latest version. Sometimes, software updates fix compatibility issues with certain apps. Head over to the Settings app, tap on "General," and then select "Software Update" to check if there's an update available.

If you were able to change the date once can you change it back to what it was? If so and Pages opens it I would copy and paste that document into a new one.