pdfpun: 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/pdfpun - from package: pdfjam

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

On Debian possible default full paths are:

/usr/bin/pdfpun - from package: texlive-extra-utils

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

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