gnome-doc: 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/gnome-doc - from package: gnome-libs-devel

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