Pages needs authentification

By authentication, do you mean a password prompt? Is this a Pages document you previously created on the same Mac and saved on the local drive, or was it previously created on another Mac with a password? Was it saved to Microsoft's OneDrive? If the latter, it was automatically encrypted and you would need the current Microsoft OneDrive application installed as the decrypting conduit back to your Mac.

If the document was created by you, in the same user account, and without a password, I don't see why Pages shouldn't just open it.

Unless for some reason, you restored a Pages document from a Time Machine backup where the previous owner user id was different than your current one. Then the ownership or group wouldn't match and Pages would throw an authentication challenge.