LOL!
I was a bit too young to sneak into the cinema to watch The Exorcist when it first came out but my dad bought the book on release and he kept secreted in his wardrobe.
Of course I found it and would retrieve back to my bedroom and speed read bits of it.
It scared me to death and I can still remember the ominous feeling it gave me as any little creak or sound in the house made the hairs on the back of my neck stand up!
Looking back on the book, it wasn't particularly well written, far too much punctuation as I remember.
I know the film you mention "The Blackcoat's Daughter"...not a bad watch at all.