pdp8: 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/pdp8 - from package: simh

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

Error in other languages:
pdp8: bevel nie gevind nie
pdp8: comandă negăsită
pdp8: comando não encontrado
pdp8: commande introuvable
pdp8: command not found
pdp8: käsku ei ole
pdp8: không tìm thấy lệnh
pdp8: komanda nerasta
pdp8: Kommando nicht gefunden.
pdp8: kommandot finns inte
pdp8: komut yok
pdp8: nie znaleziono polecenia
pdp8: níor aimsíodh an t-ordú
pdp8: no se encontró la orden
pdp8: no s'ha trobat l'ordre
pdp8: opdracht niet gevonden
pdp8: parancs nem található
pdp8: perintah tidak ditemukan
pdp8: príkaz nenájdený
pdp8: příkaz nenalezen
pdp8: команда не найдена
pdp8: командата не е открита
pdp8: 命令找不到
pdp8: コマンドが見つかりません