Here we will see that how to use RichTextBox control.
RichTextBox control
The RichTextBox control that supports rich
formatting, automatic line wrapping, HTML and RTF import/export, table support,
images and more.
For example
Drag and drop three TextBlock,three Button control on
the form.
The window form looks like this.

Figure1.gif
XAML code
<Window
x:Class="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>
<Canvas
x:Name="LayoutRoot"
Background="White">
<StackPanel
Orientation="Horizontal"
Canvas.Left="0"
Canvas.Top="20"
Height="30"
Width="184">
<Button
x:Name="makeBold"
Width="47"
Height="23" Margin="10, 2, 2, 2"
ToolTipService.ToolTip="Bold">
<TextBlock
x:Name="boldText"
Text="B"
FontFamily="Arial"
FontSize="14"
FontWeight="Bold"
HorizontalAlignment="Center"
VerticalAlignment="Center"
/>
</Button>
<Button
x:Name="makeItalic"
Width="55"
Height="23"
Margin="2"
ToolTipService.ToolTip="Italic">
<TextBlock
x:Name="italicText"
Text="I"
FontFamily="Arial"
FontSize="14"
FontStyle="Italic"
HorizontalAlignment="Center"
VerticalAlignment="Center"
/>
</Button>
<Button
x:Name="makeUnderline"
Width="56"
Height="20"
Margin="2"
ToolTipService.ToolTip="Underline">
<TextBlock
x:Name="underlineText"
Text="U"
FontFamily="Arial"
FontSize="14"
TextDecorations="Underline"
HorizontalAlignment="Center"
VerticalAlignment="Center"
/>
</Button>
</StackPanel>
<RichTextBox
Height="136"
Name="RichTextBox2"
Width="289"
Canvas.Left="20"
Canvas.Top="69"
>
</RichTextBox>
</Canvas>
</Grid>
</Window>
Now run the application and enter the text into RichTextBox control.

Figure2.gif
Now select the text and apply Bold on the text.

Figure3.gif
Similarly, we can test for Italic and underline text.