cdfhdy3d: 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/cdfhdy3d - from package: cdftools

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

Error in other languages:
cdfhdy3d: bevel nie gevind nie
cdfhdy3d: comandă negăsită
cdfhdy3d: comando não encontrado
cdfhdy3d: commande introuvable
cdfhdy3d: command not found
cdfhdy3d: käsku ei ole
cdfhdy3d: không tìm thấy lệnh
cdfhdy3d: komanda nerasta
cdfhdy3d: Kommando nicht gefunden.
cdfhdy3d: kommandot finns inte
cdfhdy3d: komut yok
cdfhdy3d: nie znaleziono polecenia
cdfhdy3d: níor aimsíodh an t-ordú
cdfhdy3d: no se encontró la orden
cdfhdy3d: no s'ha trobat l'ordre
cdfhdy3d: opdracht niet gevonden
cdfhdy3d: parancs nem található
cdfhdy3d: perintah tidak ditemukan
cdfhdy3d: príkaz nenájdený
cdfhdy3d: příkaz nenalezen
cdfhdy3d: команда не найдена
cdfhdy3d: командата не е открита
cdfhdy3d: 命令找不到
cdfhdy3d: コマンドが見つかりません