gnome-doc-prepare: 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/gnome-doc-prepare - from package: gnome-doc-utils

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

On Debian possible default full paths are:

/usr/bin/gnome-doc-prepare - from package: gnome-doc-utils

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

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