A. You buy from your local document outlet's online store, same as always (see a list of outlets selling SignaSur here). You enroll and purchase document credits through it. 

What changes is what you receive: instead of a PDF download code and a physical copyright seal, you get instant access to the digital contract on the platform, with the official copyright seal embedded automatically. When it comes time for your annual renewal, you do that through your outlet's store again (renewals are not automatic).