OrtizOL. Ventana escrita en XAML.

Ventana.xaml

<Window x:Class="R721WPFEnWindowsForms.VentanaWPF"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Ventana WPF" Height="200" Width="300">
    <StackPanel Margin="20">
        <TextBlock FontSize="20" Text="Ventana WPF" TextAlignment="Center"/>
        <Button Click="btnCerrar_Click" Content="Cerrar" Margin="50" 
                MaxWidth="50" x:Name="btnCerrar" />
    </StackPanel>
</Window>