DNI on registration form

[Shella]

Hi, I'm trying to add the filed DNI on the registration form?
As default I can't see it and I can't find it even in the admin panel.
Is possible that to add this feature I have to edit the code?

Prestashop version 1.4.1.0


P.S Is possible that there is no SEARCH in this forum?!?!

Thanks.

Shella