The critical difference between a proofreader and other types of editors is the scope of their jobs. In print publishing, the proofreader doesn’t just root out spelling and grammar errors; they also focus on aesthetic elements, like page design and typesetting.
If there is a table of contents, a proofreader will cross-check numbers and chapter names. For books with photos, they’ll check captions for style and accuracy, correct placement, and verify that credit is provided where required. To proofread a book involves a great deal of responsibility — it is the “final sweep” that will determine whether it is up to professional standards.