The Illustrated Manual is a companion quest on The Outer Worlds.
Retrieve the journal Edit
Go to the Collectors Domicile at the Abandoned Outpost in Emerald Vale, where the Stranger will encounter a few marauders and a Tamed Canid. Having disposed of the enemies, find your way to the building marked “Cannery” and get inside the room behind the cash register, where you’ll find a computer pad which directs you towards a “cave by the river”. Following the quest marker, you will end up at the Cave Entrance just east of the Geothermal Plant.
Once inside the cave, keep walking until you find a crevice to your right and discover the River Hideout, which has a number of mines inside it. Blow them up, then go inside and unlock the safe. If you don't have the required tools to open the safe you can pick them up right next to it. Retrieve the book and go back to talk to Vicar Max.
Before exiting the cave, you will notice a number of enemy markers. These are Primals waiting for the Stranger. If wanting to avoid these, just head for the opposite cave entrance.
Upon your return, Max will be furious about the book being in French, as it shows that he had hoped it to be able to help him solve “the Plan”. The book was the only reason why he got himself assigned to Emerald Vale, where he feels nothing but utter contempt for the locals. Max will ask to join your crew in order to get off the planet and thus become available as a companion, waiting for you at the Unreliable, if you accept, once you have fixed the power regulator.