<RichTextBox HorizontalAlignment="Left" Height="300" Margin="208,111,0,0"

VerticalAlignment="Top" Width="300" >

<FlowDocument>

<Paragraph>

<Run Text="Привет ворд"/>

</Paragraph>

<Paragraph>

<Run Text="парам пам пам"/>

</Paragraph>

</FlowDocument>

</RichTextBox>