coqdoc: 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/coqdoc - from package: coq

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

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