qdoc3: 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/qdoc3 - from package: qt-devel
/usr/lib64/qt4/bin/qdoc3 - from package: qt-devel
/usr/lib/qt4/bin/qdoc3 - from package: qt-devel

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

On Debian possible default full paths are:

/usr/bin/qdoc3 - from package: qtchooser
/usr/lib/x86_64-linux-gnu/qt4/bin/qdoc3 - from package: qt4-dev-tools

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

Error in other languages:
qdoc3: bevel nie gevind nie
qdoc3: comandă negăsită
qdoc3: comando não encontrado
qdoc3: commande introuvable
qdoc3: command not found
qdoc3: käsku ei ole
qdoc3: không tìm thấy lệnh
qdoc3: komanda nerasta
qdoc3: Kommando nicht gefunden.
qdoc3: kommandot finns inte
qdoc3: komut yok
qdoc3: nie znaleziono polecenia
qdoc3: níor aimsíodh an t-ordú
qdoc3: no se encontró la orden
qdoc3: no s'ha trobat l'ordre
qdoc3: opdracht niet gevonden
qdoc3: parancs nem található
qdoc3: perintah tidak ditemukan
qdoc3: príkaz nenájdený
qdoc3: příkaz nenalezen
qdoc3: команда не найдена
qdoc3: командата не е открита
qdoc3: 命令找不到
qdoc3: コマンドが見つかりません