Is there any way to search for a particular word inside a book? for example search for Mary in the book "Outlines of dogmatic theology" or find the word "Peter" inside the book "Summa theologica".
Welcome to the forums. Yes, there are three ways.
1. Use the Find in option of the Resource Menu - click on icon of resource to open. This will only do a straight text match - it's quick but the others are full featured searchs
2. search open resources
3. search specific resource
