This one’s pretty easy: pouring something over a book would mean spilling something on it. Poring over a book means reading it with great attention. “Pour” and “pore” are never interchangeable; they are two completely different words.
What type of verb is pouring?
to serve a drink by letting it flow from a container into a cup or glass pour (something) Will you pour the coffee? Should I pour? pour something out I was in the kitchen, pouring out drinks.