amd64\msgencol.ppd

PostScript Printer Description Reference

A .ppd file is a PostScript Printer Description. The plain-text file describes the features of one PostScript printer: trays, duplex, fonts, and resolution. Print systems on Windows, macOS, and Unix read PPD files to build the driver user interface. Printer makers ship the files with their drivers. Adobe defined the format.

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.