fix-qdf: 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/fix-qdf - from package: qpdf

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

On Debian possible default full paths are:

/usr/bin/fix-qdf - from package: qpdf

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

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