AboutWindow.xaml

<Window x:Class="Calculator.AboutWindow"
        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:Calculator"
        mc:Ignorable="d"
        Title="About Calculator" Height="300" Width="300" ResizeMode="NoResize">
    <Grid>
        <Label x:Name="label" Content="Калькулятор" HorizontalAlignment="Left" Margin="51,10,0,0" VerticalAlignment="Top" Height="48" Width="164" FontSize="26.667" TextOptions.TextFormattingMode="Display"/>
        <RichTextBox x:Name="richTextBox" Height="132" Margin="10,63,10,0" VerticalAlignment="Top" IsEnabled="False">
            <FlowDocument/>
        </RichTextBox>
        <Button x:Name="linkButton" Content="Просмотр исходного кода" HorizontalAlignment="Left" Margin="51,200,0,0" VerticalAlignment="Top" Width="186" Height="28" Click="linkButton_Click"/>
        <Button x:Name="closeButton" Content="Закрыть" HorizontalAlignment="Left" Height="25" Margin="203,233,0,0" VerticalAlignment="Top" Width="66" Click="closeButton_Click"/>

    </Grid>
</Window>