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.
Xpdf includes several programs that don't require the X Window System, including programs which extract images from PDF files or convert PDF to PostScript or text.
Xpdf is also used as a backend for other PDF reader frontends such as KPDF and GPDF, and its engine, sans the X11 display components, is used for PDF viewers including BePDF on BeOS, !PDF on RISCOS and PalmPDF on Palm OS.
Poppler was created based on the rendering library xpdf 3.0 for easier reuse in other programs. Many programs (including xpdf) can use poppler as their backend renderer.