While it is possible to download movies from Putlocker for free, it is illegal to do so. Downloading copyrighted movies without the express permission of the copyright owner is illegal from any website, and Putlocker provides online access to pirated versions of films.
Putlocker.com is, as of 2014, rebranded as FireDrive, but there are other piracy websites currently operating under the Putlocker name. One such site is Putlocker.is, which the U.S. government listed in 2015 as a notorious piracy marketplace. In 2013 and 2014, U.S. Trade Representative Michael Froman listed FireDrive among 23 other sites as a notorious piracy marketplace. Since 2015, FireDrive is no longer listed as "notorious," not because it has stopped engaging in illegal activities, but due to a significant drop in traffic.
Owning a copy of a film without paying for it is generally considered illegal, unless the copyright holders have granted permission. Since the copyright holders of the material on FireDrive and Putlocker.is have not granted any permission for those sites to upload their films, downloading from those sites for free is considered a copyright violation. Streaming from those sites is, however, a legal gray area.