pbmupc: 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/pbmupc - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmupc - from package: netpbm

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

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