I thought this one was kind of easy.
It was The Dunwich Horror, based on H.P. Lovecraft, and adapted by future Oscar-winner Curtis Hanson.
The cast includes former youth star Sandra Dee, former child-actor and future Oscar nominee Dean Stockwell, Oscar nominees Talia Shire and Sam Jaffe, and Oscar winner Ed Begley.
In the film Ed Begley discusses the Necronomicon, a book that shows up in a lot of horror movies and stories.