How to get the Name and Nif of a certificate encoded in base64

I am trying to get the Name and Nif of a base64 encoded certificate. I used the following code:

byte[] decbuff = Convert.FromBase64String(cert);
string result = System.Text.Encoding.UTF8.GetString(decbuff);

But the code returns the certificate fields correctly, but not the XML tags. That is, instead of returning, etc. returns for example "\ u0006 \ u0003U \ u0004 \ u0003 \ f \ u0019".

How can I get the XML?

Thank you very much.