The feat strongly implies that a Wizard could use it to learn and scribe a spell that he's unable to find a copy of to study. If your DM thinks otherwise, then you can use Extra Spell to learn a spell, then cast Secret Page
to turn the text of another spell into that one, and then copy it into your book from there if necessary. The next time you gain a level, use the retraining rules in PH2 p192-193 to switch out Extra Spell for another feat, as you've already got a copy of it now.
I've actually played in a game where the DM decided that Wizards don't automatically learn new spells when they level up, every spell must be discovered and studied. I played a Sorcerer.