Move backwards without going outside and enlarge the chain which dropped.

Get the padlock.

Enlarge the padlock and get the latch.

Open the elevator door and move to the rear door.

Remove the screws at the 4 corners with the latch and get the iron plate.

Turn over the iron plate and get the paper fragment.

If you paste the paper fragment onto the torn page of the book, you can go outside the world of the book. However, it is an imperfect world as the book pieces are insufficient.

Enlarge the book on the desk and tap the picture inside the book to return to the world inside the book again.