Recover Pages Password

From the Dock, Launchpad : Other : Keychain Access.

Select the Passwords category

1. Look for the specific Pages document name that you cannot remember the password
2. Right-click/Control-click/two-finger tap on the filename to select Get Info from the secondary menu
3. Click the Show password checkbox
   1. Enter your login password in the password prompt, and click Allow.
   2. Your document password is now shown in the Show password field.

If your document is not in the Keychain Access Passwords list of items, then you are out of luck, as there is no means to recover the document password beyond your mental recall, or the written, offline password logbook that you should be keeping in a safe place.