This format was created by Nokia for use in its proprietary phones. A bitmap image was used to transfer image files between devices over a wireless connection. It was mainly used when exchanging multimedia text messages that support inserting pictures.
PGM is a storage format for grayscale images. Files in this format can be opened using software: ACDSee Photo Manager 14, ACD Systems Canvas 15, Corel PaintShop Pro X4. This type of file can be edited with a text editor. PGM files can be in two versions: P2 / P5. P2 are readable, P5 - to binary formats.