This documentary opens on an extreme close-up of its subject’s face, skin pale and stretched tighter than a snare drum. Yet the movie isn’t out to show us the woman behind the showbiz mask, showing instead that the woman is the mask---that the “real” Joan Rivers is the cackling, crass comedienne onstage. The film follows the 75-year-old Rivers over the course of a trying year in her career, as she books afternoon stand-up slots at Bronx clubs, mounts an ill-fated play and appears on Celebrity Apprentice. She’s profane, self-deprecating and painfully insecure throughout, fearful that the blank spots in her calendar will never fill up. Rivers is a fame monster, but a funny and hardworking one, so it’s hard not to cheer for her.