This guide to expertise at thievery is so learned and erudite that any single thief who reads it and then spends 1 month thereafter practicing the skills therein will gain experience points sufficient to place him or her at the mid-point of the next higher level. 

The text disappears after reading, but knowledge is retained for 3 months—as with other magical texts of this sort, the knowledge cannot be recorded or told of, however. Any additional reading of a like manual is of no benefit to the same character.

Assassins who read the work will gain but 5,000 additional experience points after the contents have been read and pondered for 1 week.

Fighters, magic-users, and monks will not comprehend the work. 

Clerics, rangers, and paladins who read even a word of the book take 5-20 hit points of damage, are stunned for a like number of rounds, and if a saving throw versus magic is failed, they lose 5,000-20,000 experience points as well. In addition, such characters must atone within 1 day or lose 1 point of Wisdom.

Special Note. All magical books, librams, manuals, tomes, etc. appear to be "normal" works of arcane lore. Each is completely indistinguishable from the other by visual examination of the outer parts or by detection for magic aura. 

Bard characters will have normal chances of finding out the nature of such writings, as will an identify spell from a magic-user. 

Otherwise, only a wish will be useful in typing a magical writing, i.e. alter reality, commune, contact higher planes, limited wish, true seeing, true sight, and other spells or powers are useless. 

A wish will reveal general contents of a book, telling what characteristics or class is most affected (not necessarily benefited) by the work. It requires a second wish to determine exact contents. 

After being perused by a character, most of these magical works will vanish forever, but those which are non-beneficial to the reader will typically be attached to the character, and he or she will be unable to be rid of it. 

If the work benefits another alignment of character, the possessor is geased to conceal and guard the writing. 

As Dungeon Master you should use your judgment and imagination as to exactly how these items will be treated, using the rules herein as parameters.