pbmtopi3: 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/pbmtopi3 - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmtopi3 - from package: netpbm

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

Error in other languages:
pbmtopi3: bevel nie gevind nie
pbmtopi3: comandă negăsită
pbmtopi3: comando não encontrado
pbmtopi3: commande introuvable
pbmtopi3: command not found
pbmtopi3: käsku ei ole
pbmtopi3: không tìm thấy lệnh
pbmtopi3: komanda nerasta
pbmtopi3: Kommando nicht gefunden.
pbmtopi3: kommandot finns inte
pbmtopi3: komut yok
pbmtopi3: nie znaleziono polecenia
pbmtopi3: níor aimsíodh an t-ordú
pbmtopi3: no se encontró la orden
pbmtopi3: no s'ha trobat l'ordre
pbmtopi3: opdracht niet gevonden
pbmtopi3: parancs nem található
pbmtopi3: perintah tidak ditemukan
pbmtopi3: príkaz nenájdený
pbmtopi3: příkaz nenalezen
pbmtopi3: команда не найдена
pbmtopi3: командата не е открита
pbmtopi3: 命令找不到
pbmtopi3: コマンドが見つかりません