cdfhdy: 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/cdfhdy - from package: cdftools

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

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