pnmtotiffcmyk: 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/pnmtotiffcmyk - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmtotiffcmyk - from package: netpbm

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

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