We're not sure what you mean? We don't have any DRM, and any DRM built into your files should remain intact regardless of whether the buyer downloads the file or receives it on a physical disc.
If you're referring to our PDF Stamping feature being used together with SwiftCD, please see our section on combining integrations here:
http://www.e-junkie.com/ej/help.integration.htm#combining
Note that we can only stamp the PDF a buyer actually downloads directly from us; we have no influence over whatever original files you may provide to SwiftCD.