The PGM file extension is related to the OPENTECH set-top boxes. The *.pgm file stores some kind of data used by OPENTECH STBs.
PGM file extension - OPENTECH STB data file
What is pgm file? How to open pgm files?
File type specification:
The PGM file extension is used in some software for some types of set-top-boxes produced by companies like OPENTECH.
A set-top box (STB) is a device that connects to a television and an external source of signal, turning the signal into content which is then displayed on the television screen.