Everybody knows the Venn diagram of people who like reading
Use a sharp knife and a metal straightedge, carefully cut out a few pages at a time, make sure to remove small bits and pieces along the way.
After reaching the desired depth,seal the inside edges with Mod Podge and allow it to dry completely.
use Mod Podge around the top edges and glue the extra front page on top. After a few minutes,use the knife to cut out the center. This top page gives it a good clean look.