XPDF091, Software, X11 Reader for Adobe PDF files Xpdf is a viewer for Portable Document Format (PDF) files. (These are also sometimes also called 'Acrobat' files, from the name of Adobe's PDF software.) Xpdf runs under the X Window System on UNIX, VMS, and OS/2. For this Freeware CD Demo, there are two Alpha executables, one for OpenVMS v6.2 and one for v7.1.