X509Store certStore = new X509Store(StoreLocation.LocalMachine);
   certStore.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);
   X509Certificate2Collection collection = (X509Certificate2Collection)certStore.Certificates;
   var certs = collection.Find(X509FindType.FindByThumbprint, thumbprint, false);
   if (certs != null && certs.Count > 0)
   {
       normalDocument = Smev3XmlSign.SignXmlFile(normalDocument, certs[0]);
   }
   else
   {
       throw new Exception(string.Format("Сертификат с отпечатком {0} в сертификатах локального компютера не найден", thumbprint));
   }