The Book is an item that may be requested by other fellow inmates as a favour for money, or can be crafted. It can be used for the Librarian job in select prisons.
They can be found in inmate's desks and bought by fellow inmates. The Book can also be given to other inmates in order to raise their opinion of you.
It can additionally be used to make a Padded Inmate Outfit or a Sock Mace. Note that the items created with the book will be confiscated.