How can I repair a large hole in an interior door?
To be honest, I would seriously consider replacing the door. Sometimes the &quot;big&quot; fix turns out to be the cheapest &amp; easiest, particularly if the door is a typical indoor door and a standard size (or close enough that you can get a standard size door and trim it to fit).
However, one possibility that might work is a door reinforcer:

But (a) it will look a little out of place on a bedroom door and (b) I am a bit concerned about whether the lock will work effectively (and not just fall apart, or even worse, jam) because it is barely hanging on right now.