hpw to start a page from inside a window method

Ok, the thing is that the Page control can only be shown in a Frame or a NavigationWindow when using a WPF application, so what you need to do is:

In the Window XAML you need to add a Frame control as shown bellow:

<Window x:Class="WpfTestPageQuestion.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Button Content="Load Page" Click="show_page_Click"/>
        <Frame Grid.Row="1" x:Name="frame"/>
    </Grid>
</Window>

Then you need to add the handler for the Click Event for the button click:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void show_page_Click(object sender, RoutedEventArgs e)
    {
        MessageBox.Show("This should open the -page- window");

        // Start the Page control
        var mypage = new Page();
        // Set a Background to make a little more visible the change
        mypage.Background = Brushes.Red;
        // Add any content to your Page
        mypage.Content = new TextBlock
        {
            Text = "Hello from the Page!",
            FontSize = 30,
            VerticalAlignment = System.Windows.VerticalAlignment.Center,
            HorizontalAlignment = System.Windows.HorizontalAlignment.Center
        };

        // Add the Page instance to the Frame contained in the Window XAML
        frame.Content = mypage;

        // Happy message saying that we have successfully addend the Page
        MessageBox.Show("Page shown =D");
    }
}

And you are done. A Page content addent to the Window.

Hope this helps.

All Best

Raul Mainardi Neto