Convert a PPM image to a BMP file. More information: https://netpbm.sourceforge.net/doc/ppmtobmp.html.
ppmtobmp path/to/file.ppm > path/to/file.bmp
ppmtobmp -windows|os2 path/to/file.ppm > path/to/file.bmp
ppmtobmp -bbp 1|4|8|24 path/to/file.ppm > path/to/file.bmp