pi1toppm: 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/pi1toppm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pi1toppm - from package: netpbm

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

Error in other languages:
pi1toppm: bevel nie gevind nie
pi1toppm: comandă negăsită
pi1toppm: comando não encontrado
pi1toppm: commande introuvable
pi1toppm: command not found
pi1toppm: käsku ei ole
pi1toppm: không tìm thấy lệnh
pi1toppm: komanda nerasta
pi1toppm: Kommando nicht gefunden.
pi1toppm: kommandot finns inte
pi1toppm: komut yok
pi1toppm: nie znaleziono polecenia
pi1toppm: níor aimsíodh an t-ordú
pi1toppm: no se encontró la orden
pi1toppm: no s'ha trobat l'ordre
pi1toppm: opdracht niet gevonden
pi1toppm: parancs nem található
pi1toppm: perintah tidak ditemukan
pi1toppm: príkaz nenájdený
pi1toppm: příkaz nenalezen
pi1toppm: команда не найдена
pi1toppm: командата не е открита
pi1toppm: 命令找不到
pi1toppm: コマンドが見つかりません