ppmpat: 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/ppmpat - from package: netpbm-progs

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

On Debian possible default full paths are:

/usr/bin/ppmpat - from package: netpbm

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

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