An EMP3 file is usually an audio book standard format used by some websites to deliver content. In most of the cases these files are delivered to you after purchasing. The fact is that these Encrypted M-PEG Audio Level III files can be played in most of the audio players. The encryption is just a security layer preventing you to remove certain META data. The header is the same as an MP3 file and using Total Commander or a utility that allows you to view extensions, you can change EMP3 to MP3 by removing the e letter and the file will be compatible with your audio players.