This format is used as the color palette format for a variety of operating system image editors. It is used to store font templates in text and graphic editors. It allows you to change color intensity and transparency levels.
PBM is a Portable image in black and white. Can be opened with programs: Adobe Photoshop CS, ACD Systems Canvas 15, ACD Systems ACDSee 17, Newera Graphics Converter Pro, Corel PaintShop Pro X6. File contains 1 bit per pixel. PBM is a kind of file format PPM. And can be readable or binary.