Basically, as long as Ryner's eyes are on the paper, he won't be able to read the last chapter.

If he hands the book over to someone else, they'll be able to read the last chapter no problem. They could even read said chapter aloud to him. But the moment Ryner tries to catch a glimpse of the text through whatever machinations he might think of (glancing over someone's shoulder, a complex set-up of mirrors) the text is gone.