ppdfilt is a filter program designed to be used within a filter script or from the command line tool to insert printer specific commands to a PostScript print job. This can be used to tell the printer to duplex or staple the print job, or tell it what paper tray to draw paper from. In the GNULpr printing environment, users do not call ppdfilt directly, but its features are accessed by using 'lpr' or 'gpr' (see)