pnmtotiff: 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/pnmtotiff - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmtotiff - from package: netpbm

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

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