Once you can enter Pitax, go to the port and the tavern. You'll be approached by a pirate. He wants you to help a mutiny. Do Not Do That. Talk to the captain and ask why he won't sail to receive a quest, “The Impatient Pirates of Pitax”. Talk to the pirate Blutmond in the corner, near the fireplace. With Perception and persuasion, convince him to give you the location and key.
Now, travel to the Middle of Nowhere, just north of Pitax, and interact with the door. Talk to the wizard and convince him to finish the book in the way you prefer. This will take a few hours, and when it's done, you will be attacked by devils. Defeat them, and claim the book to unlock the achievement.