About ppd files, Defined, And postscript printing – Adobe Acrobat 7 Professional User Manual
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About PPD files
A PostScript Printer Description (PPD) file customizes the behavior of the printer driver
for your specific printer. A PPD file contains information about the output device,
including printer-resident fonts, available media sizes and orientation, optimized screen
frequencies, resolution, and color output capabilities. Selecting the PPD file that
corresponds to your PostScript printer or imagesetter provides the Advanced Print Setup
dialog box with the available settings for the output device, and determines which
PostScript information to send to the printer when printing a document. For example,
fonts listed in your PPD file reside in the printer, so they are not downloaded when you
print, unless you explicitly include them.