The Secret Life of Walter Mitty (1947)

Walter Mitty, a daydreaming writer with an overprotective mother, likes to imagine that he is a hero who experiences fantastic adventures. His dream becomes reality when he accidentally meets a mysterious woman who hands him a little black book. According to her, it contains the locations of the Dutch crown jewels hidden since World War II. Soon, Mitty finds himself in the middle of a confusing conspiracy, where he has difficulty differentiating between fact and fiction.

Source: TMDb