According to Webasto's documentation, Webasto is not an OEM supplier for the heating system in the A4. While there are installation guides available for the A4, these refer to heating systems from the accessories range, not to original equipment.
It might be helpful to send an email inquiry to Audi and possibly to the standard STH suppliers.
EDIT: I just Googled 'ARDIC auxiliary heater.' It seems to be a manufacturer. And if you already have the sticker on the hood, then it's definitely from them.
EDIT2: The second Google result showed that you had already discussed this topic here: http://www.motor-talk.de/t457725/f161/s/thread.html and received corresponding answers.
Why are you asking me via PM to send you Webasto documents, when it's now so obvious that you don't have any of them? I honestly find that quite rude. And I'm also putting in the effort

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Tüs.
-Private