pnmtofits: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/pnmtofits - from package: netpbm-progs

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/pnmtofits - from package: netpbm

You may install the required package with command apt-get install {package}

Error in other languages:
pnmtofits: bevel nie gevind nie
pnmtofits: comandă negăsită
pnmtofits: comando não encontrado
pnmtofits: commande introuvable
pnmtofits: command not found
pnmtofits: käsku ei ole
pnmtofits: không tìm thấy lệnh
pnmtofits: komanda nerasta
pnmtofits: Kommando nicht gefunden.
pnmtofits: kommandot finns inte
pnmtofits: komut yok
pnmtofits: nie znaleziono polecenia
pnmtofits: níor aimsíodh an t-ordú
pnmtofits: no se encontró la orden
pnmtofits: no s'ha trobat l'ordre
pnmtofits: opdracht niet gevonden
pnmtofits: parancs nem található
pnmtofits: perintah tidak ditemukan
pnmtofits: príkaz nenájdený
pnmtofits: příkaz nenalezen
pnmtofits: команда не найдена
pnmtofits: командата не е открита
pnmtofits: 命令找不到
pnmtofits: コマンドが見つかりません