py3rsa-encrypt-bigfile: 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/py3rsa-encrypt-bigfile - from package: python3-rsa

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

Error in other languages:
py3rsa-encrypt-bigfile: bevel nie gevind nie
py3rsa-encrypt-bigfile: comandă negăsită
py3rsa-encrypt-bigfile: comando não encontrado
py3rsa-encrypt-bigfile: commande introuvable
py3rsa-encrypt-bigfile: command not found
py3rsa-encrypt-bigfile: käsku ei ole
py3rsa-encrypt-bigfile: không tìm thấy lệnh
py3rsa-encrypt-bigfile: komanda nerasta
py3rsa-encrypt-bigfile: Kommando nicht gefunden.
py3rsa-encrypt-bigfile: kommandot finns inte
py3rsa-encrypt-bigfile: komut yok
py3rsa-encrypt-bigfile: nie znaleziono polecenia
py3rsa-encrypt-bigfile: níor aimsíodh an t-ordú
py3rsa-encrypt-bigfile: no se encontró la orden
py3rsa-encrypt-bigfile: no s'ha trobat l'ordre
py3rsa-encrypt-bigfile: opdracht niet gevonden
py3rsa-encrypt-bigfile: parancs nem található
py3rsa-encrypt-bigfile: perintah tidak ditemukan
py3rsa-encrypt-bigfile: príkaz nenájdený
py3rsa-encrypt-bigfile: příkaz nenalezen
py3rsa-encrypt-bigfile: команда не найдена
py3rsa-encrypt-bigfile: командата не е открита
py3rsa-encrypt-bigfile: 命令找不到
py3rsa-encrypt-bigfile: コマンドが見つかりません