From publisher blurb:
Wizards stand apart from other magic-users in how they acquire arcane knowledge. Rather than drawing on inborn talent or making some fell bargain with an otherworldly power, wizards discover magic through research and study. They delve into ancient tomes and riffle through crumbling scrolls, committing to memory all that they have learned. Their methods reward them with incredible versatility but also tempt them to peer into dark places, to learn and master the most secret arts, for there lies true and lasting power, even if its knowledge damns their souls.
Forbidden Knowledge adds seven new arcane traditions to the wizard class. Each tradition reflects a sinister avenue of study and research, offering ways to gain unique and terrible magic in exchange for madness, corruption, or worse. Using the options in this supplement, player characters can conjure up demons, bestow wicked curses, and reach beyond the bounds of reality to commune with the insane powers that screech and thrash in the primordial void. If you seek advantage against rivals and eldritch weapons to destroy enemies, that knowledge awaits you!