PD, FlexiSIGN 5 Plotter Document (.pd)
The PD Vector image file format
PD files can be associated with a number of programs. The more common one is FlexiSIGN 5, a program that allows you to create all kinds of signs for commercial purposes. The PD files created using said program contain graphic data in a vector graphic format. It's comparable large in size so that the design can be printed easily on cutters and vinyl plotters.
Technical details of PD files
Since PD files contain vector graphic data, it can be resized without quality loss. However, the designs can also contain text and raster graphics which do not do well when being scaled to become bigger. PD files, however, are also associated with PipeDream. In this case, the PD file contains spreadsheet as well as word processing information. In other instances, PD files are used to store data in the Perl Data Language.