import a digital signature installed in browser to sign and encrypt files

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ASP.NET

C#5.0

I had an project in which earlier the files were used to get signed using.pfx files but not the organisation has E-Tokens(usb device) when plugged in the computer, the files get certificates are used in to the browsers, now i am not able to figure out a way of importing the certificate from the browser to digitally sign a PDF file and then encrypt the excel file using that certificates.

I wish any one can help by giving me a code or reference.