texdoctk: 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/texdoctk - from package: texlive-base

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

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