Could you suffer from post traumatic stress disorder from watching a movie?

Not usually, but: If it impinges on existing past trauma you have experienced, you may have symptoms of hypervigilance, extreme anxiety, exaggerated startle, crying spells, etc. Some movies are very violent, and revive previous memories -- or are terrifying on their own. Having a trauma response be protracted from this -- rather than acute and gradually dissipating -- is rare though.