What you omitted was if the file was found on the Pages Recents menu. Pages saves documents in the last saved folder location. Some users assume that when they start typing in a new Pages document, that it will autosave their work and when they quit Pages, all is permanently lost. I would like to believe that you had previously saved this document and the preceding sentence would not apply.
Were you saving this missing Pages document to non-Apple cloud or server filesystem services? Pages remembers where it last saved a document and will continue to do so until that location is changed. Following that reasoning, open a new Pages document and click save to see where it points to for the faux save.
I strongly recommend that anyone using Pages, Numbers, or Keynote especially have ongoing Time Machine backups to an external drive. That makes missing document recovery reasonably straightforward.
If you have your Mac configured for Spotlight indexing of Documents, then you might try the following Spotlight search from either the menu extras 🔍 Spotlight tool, or in an open Finder Window's search field. The following says find a Pages document that was used after (>) Dec 1, 2023:
kind:pages used:>12/01/2023