Other authors such as August Derleth and Clark Ashton Smith also cited it in their works; Lovecraft approved, believing such common allusions built up "a background of evil verisimilitude." Many readers have believed it to be a real work, with booksellers and librarians receiving many requests for it; pranksters have listed it in rare book catalogues, and a student smuggled a card for it into the Yale University Library's card catalog.
This a three film adoptation that is the mythos of HP Lovecraft
The Necronomicon was born of Lovecraft's fertile imagination in his 1936 essay, "A History of The Necronomicon."
The fantasy captured the imagination of some of Lovecraft's fans, and for years a belief persisted that a real grimoire titled The Necronomicon existed. Book-sellers received request for it. As the late 1980's, at least two versions of the "real" Necronomicon had been published.
The Encyclopedia Of Witches and Witchcraft by Rosemary Ellen Guiley
Necromancy - divination by raising the spirits of the dead, one of the claimed Black Arts practised by witches and magicians. The classic case of necromancy is the Witch of Endor, described in the Bible (1 Samuel 28), who summoned the spirit of Samuel in the presence of Saul. The Biblical episode was widely accepted as irrefutable evidence of the existence if Witchcraft. The idea behind necromancy was that the dead could see the future and could be conjured into describing it.
It is unlike other forms of divination in that it tools are not part of the world around us, like clouds or rods or animals. It goes back to legends of descent of the Underworld and visits from the dead, such as recorded in Shakespeare's play Hamlet, but in its trappings and rituals it is more a branch of Black Magic than of regular divination, which relies on the person of the diviner being in tune with the phenomena he or she is assessing. Nine days of morbid and grisly preparation are required in which the magician dresses in the burial clothes of corpses and recites the funeral service over to himself and his assistants. At midnight or dawn, the grave is opened and the corpse conjured to come out alive. In accounts of such events, the corpse is often made to speak through the mouth of one of the assistants.
Dictionary of the Occult - Publisher Geddes & Grisset reprinted 2002.