Film preservation and public domain status are governed by laws regulating copyright and intellectual property. It is the process of ensuring that films can be protected and maintained over time, and there are several requirements to be eligible. A film can not achieve public domain status until after the copyright owner’s death plus 75 years. If the copyright is owned by a studio, the copyright protections normally only last 95 years. That extends to films produced as work for hire. Once the copyright  expires the film achieves public domain status.