string s = "0.009";

double d = Double.Parse(s, new CultureInfo("es-ES"));

double d = 0.009D;
string formatted = d.ToString(new CultureInfo("es-ES"));

double d = Double.Parse("0,009",
    NumberStyles.AllowDecimalPoint | NumberStyles.AllowThousands,
    CultureInfo.CreateSpecificCulture("es-ES"));