obabel: 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 Debian possible default full paths are:

/usr/bin/obabel - from package: openbabel

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

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