private void btnOpenPage1_Click(object sender, RoutedEventArgs e)
{
    //// Window 열기
    //Window1 w1 = new Window1();
    //w1.Show();

    // Tip. Window 폼에서 Page 폼 열기
    NavigationWindow nw = new NavigationWindow();
    nw.Height = this.Height;
    nw.Width = this.Width;
    nw.Show();
    nw.Navigate(new Uri("Page1.xaml", UriKind.Relative));
    this.Close();
}