Digital signature to PDF with ITextSharp

The design is simple , we need a WEB example using ITextSharp and Asp.Net to sign PDFs using certificates installed on machines ( .pfx or .cert ) the User or SmartCard connected to the USB User 's Machine . (Picture 1 ) Software flow is as follows . The User selects the PDF. And click the button to sign the PDF. (Picture 2 ) At this time should be requested from the User to select the certificate to be used . ( IMAGE 3 ) After selecting the certificate and the User enter his password , the site will post the PDF to the server and will be signed when the subscription is completed the server will return the signed PDF to the User .