pnmtoxwd: 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/pnmtoxwd - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/pnmtoxwd - from package: netpbm

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

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