"retrieve password for PAGES"

On the long shot that you have been using Time Machine since you started writing your novel, you may be able to restore an older copy of that work from a time frame earlier than when you applied a document password. To do that, and if you are using Time Machine, then use /Applications/Time Machine.

Since the document does not automatically unlock within your Mac account, I suspect that you bypassed the part about asking Keychain access to remember it at the time it was set. Aside from the first paragraph, nothing on earth will unlock that document until you "remember" the password.

State to yourself that you will "clearly remember the password on that specific Pages document" and then stop trying to remember it. Your subconscious will go to work and within a day or two, you may remember it in amazement.

Well, Pages does not have a password but it would appear you password protected the document you started writing.

Password-protect a Pages document on Mac - Apple Support

Here’s the really bad news for you from that support page:

Important: There’s no way to recover your password if you forget it. Be sure to choose a password you won’t forget, or write the password down in a safe place.

Sorry