Weed seeds won't germinate through several inches of new soil. If the new soil is 'clean' then I would loosen the old soil first (rototill or fork to loosen hard packed soil) and then cover it with the new soil, followed by a layer of Mulch.
If you are worried about creating a 'transition' layer you can do some mild 'forking' afterwards, but be aware you may bring weed seeds to the surface where they will sprout.
Newspaper is used to block perennial weeds like Bermuda grass. If you have this be aware that tilling will create many root cuttings which will all sprout eventually, and may be spread over a larger area.

Thank you. He scraped off most of the weeds and we're hoping there's no bermuda grass! I appreciate your input. He actually sprayed to eradicate most of the weeds, but since it's spring they're plentiful!
LindaB/CA