This book contains lost knowledge and forbidden information that has been lost to the ages. Such a vast amount of information cannot be taken in its entirety. You must make a choice which sections of the tome you study.
If you spend 48 hours over a period of 6 days or fewer studying the book's contents and practicing its guidelines, your ability score, linked to what section you read, will increase by 2, as well as your maximum for that score.
The Tome will vanish upon your finishing the section of choice and turn up in the world again at some random place and time.