Book of Secrets

There is no official name for this story, but the whispers remain the same. There is a hidden magical world. And that world is out to get you, witches will steal your babies and your soul will serve the demons for all eternity. And it all starts - as per usual - with a book.

"No harm ever came from reading a book."

— your local librarian, quickly hiding the book on mummies she's holding"

The book is said to be written by the Hand of Evil himself and its scripture transcends all written languages. If you happened to open it and gaze on its contents, the words would slither and coil and crawl into one another, revealing their meaning in a beautiful but damning dance of ink. This is the book of secrets, the key to the universe, the place of all things unspoken. It is considered to be the single most scariest thing in the universe. Yes, surpassing those lava tentacle things your demonologist teacher warned you about. It is supposed to give you all the reasoning behind Morningstar revolting against the Almighty and turning against his own kind, resulting in a war that is supposed to last for eternity.
According to the tale, it is a record of his words he yelled back to his comrades after being struck down from Earth and cast out for good to the lower levels of Abyss. Here he laid, impaled on the mountains, but never ceasing to use his voice to corrupt others. The book of secrets is said to contain all the knowledge that he refused to let be buried with him. It contains all that must be known. But unlike the Divine Eye, also a symbol of knowledge, people do their best to avoid any mentions of this thing. There are additional rumours and tales about pages from this book being ripped out and making their way into the hand of mortals, abusing their minds and bending their will to serve the Fallen. It is said once you see the words you can never unsee them.
This is the number one story to scare people away from any book or any written medium. It is vastly used to discourage mostly poorer and less educated masses, from expanding their education for fear of being corrupted by ideas that are not of this world. It is a way of the rich to keep their upper hand over positions of power and keeping anyone else from it.
Writing is kind of magic after all.