A Practitioner's Guide to Exorcism is a book on exorcism kept in the Men of Letters bunker.
History[]
After his brother disappears, hunter Sam Winchester keeps several books on possession and exorcism on the library table of the Men of Letters bunker, including this one.
After Dean is successfully cured of being a demon, the angel Castiel briefly picks up the book while in the library. After Sam enters the room, Castiel puts down the book to talk to him.
As Roscoe and Eldon are raiding the bunker, Cyrus Frankenstein finds the book and it draws his interest. However, Roscoe orders Cyrus to put down the book as they are not there to read. Instead, Cyrus is ordered to gather anything useful and to prepare to destroy everything else. Before the Stynes can complete their mission, Dean returns and kills them, saving the book from theft or destruction.
While going to make amends with Sam over Jack, Dean finds Sam reading the book. Sam then puts it down to talk.
As the Winchesters go through the archives for clues on the Seal of Solomon, the book is one of the items Sam pulls out. Later, Sam appears to be looking through it when Dean thinks he's found something but actually hasn't.