phpdoc: command not found

Have You tried accessing the binary with the full path?

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/phpdoc - from package: php-pear-PhpDocumentor

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