The scrapbook is a confusing symbol. As we discuss in "Setting," it contains some of the crucial details of the Overlook's history from 1945 to 1967. For Jack, the scrapbook is a symbol of the novel he hopes to write. The hope of eventually writing this novel is part of the bait that keeps Jack wanting to stay at the Overlook. He desperately want to find out its secrets. The ghost of Delbert Grady, the murderous, suicidal 1970 caretaker, tells Jack that the mysterious "manager" left the scrapbook especially for Jack to find.
If the Overlook is like a criminal who wants to get caught in order to be famous, it would make sense that the Overlook would leave it for Jack to find. He's a writer who can immortalize it in print in a way the moldering news clippings and boxes of files cannot. For one thing, they're never read, except by Jack. The hotel also uses the scrapbook to toy with his aspirations, and then cruelly snatch them out of reach.
For Jack, the scrapbook also triggers his own mental scrapbook, particularly the pages featuring his father. This puts Jack in a trancelike state that sends him upstairs to destroy the radio, which is broadcasting murderous instructions from said father. The scrapbook symbolizes an extreme human powerlessness against bad memories and the potential in such memories for self destruction.