The material below is Open Game Content from a 3PP Source
Wizard Spells and Borrowed Spellbooks
A wizard can use a borrowed spellbook to prepare a spell he already knows and has recorded in his own spellbook, but preparation success is not assured. First, the wizard must decipher the writing in the book (see Arcane Magical Writings, above). Once a spell from another spellcaster's book is deciphered, the reader must make a Spellcraft check (DC 15 + spell's level) to prepare the spell. If the check succeeds, the wizard can prepare the spell. He must repeat the check to prepare the spell again, no matter how many times he has prepared it before. If the check fails, he cannot try to prepare the spell from the same source again until the next day. However, as explained above, he does not need to repeat a check to decipher the writing.