amd64\ttfsub.gpd

Generic Printer Description Reference

A .gpd file is a Generic Printer Description for the universal printer driver of Windows, Unidrv. The plain-text file describes the features and the commands of one printer model. The driver reads the file and gets the printer-specific behavior without new code. Printer makers ship .gpd files in their driver packages. PostScript printers use .ppd files in place of .gpd files.

A file extension is only a part of the file name. It does not give a guarantee about the format or the content of a file. But on Windows, the extension selects the program that opens the file.