Registrare un certificato .pfx e .cer

Good morning,

I need register some certificates .pfx e .cer on my server windows 2012, becouse I'll use them on my application C#.
I have tried to use the certificates without registered them so :

                ProxySgate = new SgateWebService();
 
                // Invio i certificati tramite il collegamento proxy web senza doverli registrare sul pc o server
                ProxySgate.ClientCertificates.Add(X509Certificate.CreateFromCertFile(pathCertificati + certificatoSGATE));
                ProxySgate.ClientCertificates.Add(X509Certificate.CreateFromCertFile(pathCertificati + certificatoGeoTrustPCA));
                ProxySgate.ClientCertificates.Add(X509Certificate.CreateFromCertFile(pathCertificati + GeoTrustEV));
                X509Certificate2 cert = new X509Certificate2(@"D:\certificatiSGATEANGIZIA\MASSIMO-SGATE.pfx", password, X509KeyStorageFlags.MachineKeySet);


but I received this error : "Network Password is not correct", so I have thought to register those certificates.