pdiff: 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/pdiff - from package: a2ps

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

On Debian possible default full paths are:

/usr/bin/pdiff - from package: a2ps

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

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