NPS as DHCP

Yes, just install the DHCP role and configure.  If you have routers between your clients and the NPS you'll need to configure a relay agent on the router that clients connect to.

I have many routers between and they are not all mine. How do i configure ?

Your DSLAM can probably do it.  Configure a DHCP relay (or IP helper as it may be called) on the DSLAM which points to the IP of your NPS server.

Well, I have no access to the Dslam, I only hire access thru them. I own the backbone router and the DSL modems but the dslams are owned and runned by another company who also own the copper wire.

But as NPS can manually assign an ip address to the modem thru Dial In tab in AD, is it not possible to assign DNS ip addresses ?

You can assign DNS via RADIUS (NPS) but it's not that easy.  Perhaps a bit of an overview of how the client's traffic gets from their router to your NPS would help.

Is the DSLAM pointing at your NPS when a client attempts to connect their DSL router?  If so, do you know the manufacturer?

How can I assign DNS via NPS ?

Using vendor attributes... hence asking...

Is the DSLAM pointing at your NPS when a client attempts to connect their DSL router?  If so, do you know the manufacturer?

I don´t know the manufacture of the Dslam.

What I do now is:
I connect router and get DSL sync. Then I enter my username@domain.dot and my password for PPPoE dial in.
After that BBRAS (owned by the other company) ask RADIUS(owned by the other company) which ISP is the owner of this @domain.dot
Next the LNS(owned by the other company) asks my RADIUS(NPS) if the user is allowed. My RADIUS answers with ip address who has been set in the Dial Up tab on the AD and then my router can talk to my backbone router and go to the internet but without DNS.