pbmtoicon - convert a Sun icon image to PBM
This program is part of Netpbm(1).
pbmtoicon was obsoleted by pbmtosunicon(1), introduced with Netpbm 10.53 (December 2010). pbmtosunicon is backward compatible with pbmtoicon, plus adds additional functions, including the ability to convert a Depth=8 Sun icon, producing a PGM image.
Starting in Release 10.53, pbmtoicon is just an alias for pbmtosunicon.
The point of the name change is that there are many kinds of icons in the world besides Sun icons, and in 2010, the Sun variety isn't even common.
In releases before 10.53, you can use the pbmtosunicon documentation for pbmtoicon, as long as you recognize that any change the pbmtosunicon manual says happened in or after Netpbm 10.53 doesn't apply to pbmtoicon.