pbmtomda: 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/pbmtomda - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pbmtomda - from package: netpbm

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

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