High Quality Content by WIKIPEDIA articles! Xpdf is an open-source PDF viewer for the X Window System and Motif. Xpdf runs on practically any Unix-like operating system. Xpdf can decode LZW and read encrypted PDFs. The official version obeys the DRM restrictions of PDF files, which may prevent copying, printing, or converting some PDF files. There are patches which make Xpdf ignore these DRM restrictions.