ff3d: 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/ff3d - from package: freefem3d

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

Error in other languages:
ff3d: bevel nie gevind nie
ff3d: comandă negăsită
ff3d: comando não encontrado
ff3d: commande introuvable
ff3d: command not found
ff3d: käsku ei ole
ff3d: không tìm thấy lệnh
ff3d: komanda nerasta
ff3d: Kommando nicht gefunden.
ff3d: kommandot finns inte
ff3d: komut yok
ff3d: nie znaleziono polecenia
ff3d: níor aimsíodh an t-ordú
ff3d: no se encontró la orden
ff3d: no s'ha trobat l'ordre
ff3d: opdracht niet gevonden
ff3d: parancs nem található
ff3d: perintah tidak ditemukan
ff3d: príkaz nenájdený
ff3d: příkaz nenalezen
ff3d: команда не найдена
ff3d: командата не е открита
ff3d: 命令找不到
ff3d: コマンドが見つかりません