If you cannot find that important Pages document in iCloud, in your Trash, or elsewhere on your Mac — then it is gone. You might be able to restore that document from a previous Time Machine backup — if you had Time Machine configured and backing up to an external drive. If you weren't using Time Machine, then you have no chance for document recovery unless you previously sent it to someone, and they can send it back to you.
It is equally important to be using regular Time Machine backups — as it is to initially save a Pages document and give it a real (not Untitled.pages) name. Once you do that, Pages will enable autosave and every change to your document will be saved, and you will also have the ability to Revert any mistakes made within your document to a previous editing session.