pnmtoplainpnm - convert portable any map to plain (ASCII) anymap format
Reads a portable anymap as input, either from the named file or if no
file named, from Standard Input.
Writes out the image in plain (ASCII) anymap format to Standard Output.
Of the three plain anymap formats, this program generates the one that
corresponds naturally to the one of the three anymap formats that is
the input (PBM for PBM, etc.).