BlockUIContainer with a Button along with Paragraph
<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
HorizontalAlignment="Center" VerticalAlignment="Center">
<FlowDocumentPageViewer>
<FlowDocument>
<Paragraph>
This is a paragraph.
</Paragraph>
<BlockUIContainer>
<Button Content="Button" />
</BlockUIContainer>
<Paragraph>
This is another paragraph.
</Paragraph>
</FlowDocument>
</FlowDocumentPageViewer>
</Page>