pvtk: 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 Debian possible default full paths are:

/usr/bin/pvtk - from package: python-vtk6
/usr/bin/pvtk - from package: python-vtk

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

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