File Extension PGM File Format Portable Graymap (bitmap) PGM stands for Portable Graymap (bitmap). This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question How to know from all where a program (*PGM) is called? Avoid "black screen" between two processes in CL program How to identify caller program.