The following code creates a RichTextBox in WPF and adds a flow document to it. Code also adds a button in XAML.
<Window x:Class="RichTextBoxSample.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<Grid>
<RichTextBox Name="RTB"
Height="167" Margin="0,0,0,95"
Width="278">
<FlowDocument>
<Paragraph>
<Run>First paragraph goes
here. Type some text here.</Run>
</Paragraph>
<Paragraph>
<Run>Second paragraph goes
here. Type some text here.</Run>
</Paragraph>
</FlowDocument>
</RichTextBox>
<Button Height="36"
Margin="12,0,0,34"
Name="button1" VerticalAlignment="Bottom"
HorizontalAlignment="Left" Width="97" Click="button1_Click">Get Contents</Button>
</Grid>
</Window>
On button click event handler, which looks like following, we are going to read contents of a RichTextBox. As you can see from the code below, we use RichTextBox.ContentStart and RichTextBox.ContentEnd to get the entire content and later display in a MessageBox.
private void button1_Click(object
sender, RoutedEventArgs e)
{
TextRange
textRange = new TextRange(RTB.Document.ContentStart,
RTB.Document.ContentEnd );
MessageBox.Show(textRange.Text);
}