pbmtoybm: 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/pbmtoybm - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmtoybm - from package: netpbm

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

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