qtdoc: 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/qtdoc - from package: kdesdk

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

On Debian possible default full paths are:

/usr/bin/qtdoc - from package: kdesdk-scripts

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

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