ppdi: 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/ppdi - from package: cups

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

On Debian possible default full paths are:

/usr/bin/ppdi - from package: cups-ppdc

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

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