Quote Originally Posted by Clawtooth View Post
There's a great deal in the THM questline about the book: Thaumaturgy: The Yawning Abyss so it is likely that they do need literacy.
In Version 1.0, it was a running joke that the guild receptionist, Yayake, would threaten you with needing to memorize the contents of a very large stack of books before deciding that perhaps, for now, you might learn more in the field... this time. So, either literacy rates among adventurers are, as Ferne suggests, much higher, or she knew most people couldn't read and was just a terrible, terrible person.