The Book of the Kosst Amojan is an ancient Bajoran religious text, detailing the knowledge of the Pah-wraiths. The book is considered highly dangerous, and its viewing is restricted to the Kai alone, as it contains detailed instructions on how to release the Pah-wraiths from their imprisonment in the Fire Caves of Bajor.
In 2375, Kai Winn Adami, under coercion from Dukat - disguised as a Bajoran farmer, Anjohl Tennan - requested the book from the archives, intending to use it to free the Pah-wraiths. When opened, the book was devoid of text, which was only revealed when blood was spattered across its surface. (DS9: "The Changing Face of Evil")
The restriction on reading the Kosst Amojan was enforced by the book itself. When Dukat attempted to decipher the text, the book released a plume of energy that blinded him for several days. ("When it Rains...")
Winn and Dukat took the text to the Fire Caves, and were in the process of releasing the Pah-wraiths when they were stopped by the Emissary, Benjamin Sisko. The book was destroyed in the ensuing struggle, consumed by the fires of the Pah-wraiths. ("What You Leave Behind")