I once found a book which had information about the different powers and rituals linked to the specific entity, but I can't seem to find it nor a reference to it. Does anyone of you know about it? It could have been Dark Heresy too,..

I suspect you'll find that sort of thing in Black Crusade. Never even glanced at them myself, but if it's anywhere it'll be in one of those books.

You might be looking for the Dark Heresy book Disciples of the Dark Gods Chapter V: Malleus.

Although it will work as a good substitute neither of those are the one that I am looking for :/