PDF DRM Removal (from removedrmfromepub) is a commercial tool that allows to remove DRM from PDF ebooks.
Haven't tried to use it, since freeware epub DRM removal plug-in for
Calibre works just fine. Besides Calibre can convert PDF files to other ebooks formats, so you can read PDF ebooks whether you use
Kindle,
Sony Reader,
Nook or some other reader.
Download freeware PDF DRM removal plug-in for Calibre and standalone freeware PDF DRM removal software:
ebook DRM removal tools archive