Using Certificates with c# and ASP.NET

Hi I’m developing an internet ASP.NET application, which needs to interact with Microsoft Certification Authority Server, the

client (browser) will request a certificate to sign a file (word, pdf) later.
I'm really disoriented. Must I use CAPICOM? Signing in the server, and sending the certificate through an SSL connection? Is

there any class in the .Net Framework to interact with Certification Authority Service without CAPICOM or an external Api?

Where can i get a code example?

Regards
Sergio