Atticus does not apply DRM to ePub files. Each company that produces eReader devices and apps has its own DRM system, so it is not typically applied during the formatting stage. For example, Amazon has a specific DRM system for Kindle devices, and Barnes & Noble has its own unique DRM system for Nook devices.
If you wish to apply DRM specifically for selling directly to a customer or for ARC copies, some distributors like BookFunnel allow you to use a type of "Social DRM" that embeds the user’s email address into the file.
It's important to remember that DRM is not foolproof and can sometimes inconvenience legitimate users.