A DM file is a copy-protected media file created by the Sony Ericsson DRM Packager. The DM format is used by Sony Ericsson phones and ensures that media files can only be opened on authorized cell phones.

Sony Ericsson's DRM Packager is a tool that developers and media providers can use to protect their content. It wraps the original file in a DRM container defined by the Open Mobile Alliance (OMA), which prevents the file from being opened by unauthorized recipients.