This article has move here: WPF RichTextBox Control Tutorial
The following code snippet creates RichTextBox in XAML.
- <RichTextBox></RichTextBox>  
 The following code snippet sets the name, height and width of a RichTextBox control. The code also sets the horizontal alignment to left and the vertical alignment to top. 
- <RichTextBox Margin="10,10,0,13" Name="RichTextBox1" HorizontalAlignment="Left"   
-                  VerticalAlignment="Top" Width="500" Height="300" />  
 The following code snippet adds several items to a RichTextBox control.
- <RichTextBox Margin="10,10,0,13" Name="RichTextBox1" HorizontalAlignment="Left"   
-              VerticalAlignment="Top" Width="500" Height="300">  
-     <FlowDocument>  
-         <Paragraph>  
-             I am a flow document. Would you like to edit me?  
-             <Bold>Go ahead.</Bold>                  
-         </Paragraph>  
-         
-         <Paragraph Foreground="Blue">            
-             I am blue I am blue I am blue.    
-         </Paragraph>  
-     </FlowDocument>          
- </RichTextBox>  
 A RichTextBox control comes with spell check functionality out-of-the-box. By setting the SpellCheck.IsEnabled property to true enables spell checking in a RichTextBox. 
- SpellCheck.IsEnabled="True"  
 You can set this in code as follows:
- mcRTB.SpellCheck.IsEnabled = true;