Here's the rough outline of the book, Its been around since man has learned to read and write, it was used as a tool to corrupt mages. Until walden its succeeded in its mission. Along with Walden being a necromancer he is a powerful mage and would have been inline to join the Elder Council in Va'shar. The book shows up at random times throughout history, and in different places regardless of where it had last ended up. Once it has completely consumed the soul who studies it, it disappears. 

So its not well known, and usually drives people to seek solitude.