pbmtopsg3: 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/pbmtopsg3 - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmtopsg3 - from package: netpbm

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

Error in other languages:
pbmtopsg3: bevel nie gevind nie
pbmtopsg3: comandă negăsită
pbmtopsg3: comando não encontrado
pbmtopsg3: commande introuvable
pbmtopsg3: command not found
pbmtopsg3: käsku ei ole
pbmtopsg3: không tìm thấy lệnh
pbmtopsg3: komanda nerasta
pbmtopsg3: Kommando nicht gefunden.
pbmtopsg3: kommandot finns inte
pbmtopsg3: komut yok
pbmtopsg3: nie znaleziono polecenia
pbmtopsg3: níor aimsíodh an t-ordú
pbmtopsg3: no se encontró la orden
pbmtopsg3: no s'ha trobat l'ordre
pbmtopsg3: opdracht niet gevonden
pbmtopsg3: parancs nem található
pbmtopsg3: perintah tidak ditemukan
pbmtopsg3: príkaz nenájdený
pbmtopsg3: příkaz nenalezen
pbmtopsg3: команда не найдена
pbmtopsg3: командата не е открита
pbmtopsg3: 命令找不到
pbmtopsg3: コマンドが見つかりません