pydoc3: 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/pydoc3 - from package: python3

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

Error in other languages:
pydoc3: bevel nie gevind nie
pydoc3: comandă negăsită
pydoc3: comando não encontrado
pydoc3: commande introuvable
pydoc3: command not found
pydoc3: käsku ei ole
pydoc3: không tìm thấy lệnh
pydoc3: komanda nerasta
pydoc3: Kommando nicht gefunden.
pydoc3: kommandot finns inte
pydoc3: komut yok
pydoc3: nie znaleziono polecenia
pydoc3: níor aimsíodh an t-ordú
pydoc3: no se encontró la orden
pydoc3: no s'ha trobat l'ordre
pydoc3: opdracht niet gevonden
pydoc3: parancs nem található
pydoc3: perintah tidak ditemukan
pydoc3: príkaz nenájdený
pydoc3: příkaz nenalezen
pydoc3: команда не найдена
pydoc3: командата не е открита
pydoc3: 命令找不到
pydoc3: コマンドが見つかりません