ldrdf: 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 CentOS possible default full paths are:

/usr/bin/ldrdf - from package: nasm-rdoff

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/ldrdf - from package: nasm

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

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