The Pact Infernal

Written in Infernal by an uncredited author, this slim tome details multiple rituals that would allow an individual to contact, summon, and potentially command various devils of the Nine Hells. True to its name, it also contains information on dealing with devils, from willingly forging pacts to avoiding agreements that benefit only the devil. In contrast to the much larger Demonomicon, the Pact Infernal contains only cursory information on types of devils and their proclivities; there's enough to give a reader a better understanding, but not enough to paint a full picture of an individual devil's motives or desires. 
The Pact Infernal was found by Lucretia in the secret study, and is currently in her possession. She tried to pass the tome off to her father Alistair for safekeeping when he visited the Academy, but he advised Lucretia to keep it in case the information proved useful (while also warning her not to actually use the rituals within).

Medium

Paper