A sought after book of the occult or a grimoire.
According to Rick, of Rare Reads, it’s doesnt exist.
According to some further research, the book has many different accounts as to it’s composition and make, lending credence to the claim that the book is myth.
According to Polk Dot the Kar Dār is also known as ‘That which should not be’ and is a catalog of creation abominations that should not be/don't exist/shouldn't exist. It doesn't translate perfectly. And has somehow escaped the grasp of the demons.