It's not advisable to transfer the files from a DVD to external hard drive directly since virtually all DVD movies are copy-protected to prevent illegal distribution. Even if you successfully copy the files to an external hard drive, when you play the movie, you would find that it is incomplete or corrupt. The correct way is to use DVD copy software to remove DVD copy protection and get complete digital copies of a DVD first, and then transfer them to your device. WonderFox DVD Ripper Pro is a recommended option for this task. It can not only convert DVDs to MP4 and other video formats but also create ISO images from DVDs for backup. The following guide tells how to put DVDs on external hard drive using the software.