$ sudo apt-get update
$ sudo apt-get install imgvtopgm 

imgvtopgm is installed in your system.

Make ensure the imgvtopgm package were installed using the commands given below,

$ sudo dpkg-query -l | grep imgvtopgm *

You will get with imgvtopgm package name, version, architecture and description in a table

imgvtopgm package basic information: