DE provides legacy support for Adobe's old DRMed PDF's, but its interesting capability is support for the new .epub format. This is reflowable, and is the next generation beyond .oeb (which is the basis for .mobi and .LIT). So far as I know, DE only supports .epub without DRM at present, see
Digital Editions XHTML samples. These are currently only readable via DE or the very latest version of FBReader.