pc1toppm: 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/pc1toppm - from package: netpbm-progs

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

Error in other languages:
pc1toppm: bevel nie gevind nie
pc1toppm: comandă negăsită
pc1toppm: comando não encontrado
pc1toppm: commande introuvable
pc1toppm: command not found
pc1toppm: käsku ei ole
pc1toppm: không tìm thấy lệnh
pc1toppm: komanda nerasta
pc1toppm: Kommando nicht gefunden.
pc1toppm: kommandot finns inte
pc1toppm: komut yok
pc1toppm: nie znaleziono polecenia
pc1toppm: níor aimsíodh an t-ordú
pc1toppm: no se encontró la orden
pc1toppm: no s'ha trobat l'ordre
pc1toppm: opdracht niet gevonden
pc1toppm: parancs nem található
pc1toppm: perintah tidak ditemukan
pc1toppm: príkaz nenájdený
pc1toppm: příkaz nenalezen
pc1toppm: команда не найдена
pc1toppm: командата не е открита
pc1toppm: 命令找不到
pc1toppm: コマンドが見つかりません