This program is part of Netpbm.

pnmnoraw was replaced in Netpbm 8.2 (March 2000) by pnmto-
plainpnm,whichwasobsoletedby pnmtopnm in Netpbm 10.23 (July 2004).

pnmtoplainpnm was actually the same program; it was just renamed to
make it clear that is just a format converter.

pnmtopnm is more general, in that it can go both directions. pnmtopnm
-plain is the same as pnmnoraw.