MainWindow.xaml

<Window x:Class="TheExtensionChanger.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:TheExtensionChanger"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
	<Grid>
		<Button x:Name="btnSelectDirectory" Content="Select Directory" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="118" Click="btnSelectDirectory_Click"/>
		<TextBox x:Name="txtOriginalExtension" HorizontalAlignment="Left" Height="23" Margin="133,8,0,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="120"/>
		<TextBox x:Name="txtNewExtension" HorizontalAlignment="Left" Height="23" Margin="258,9,0,0" TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="120"/>
		<Button x:Name="btnChangeExtension" Content="Change" HorizontalAlignment="Left" Margin="383,10,0,0" VerticalAlignment="Top" Width="74" Click="btnChangeExtension_Click"/>
		<RichTextBox x:Name="txtLog" HorizontalAlignment="Left" Height="274" Margin="10,35,0,0" VerticalAlignment="Top" Width="497">
			<FlowDocument>
				<Paragraph>
					<Run Text=""/>
				</Paragraph>
			</FlowDocument>
		</RichTextBox>
	</Grid>
</Window>