A ScrollViewer is a container that can display content that is larger than the ScrollViewer itself. However by default the Scroll Viewer displays a Vertical Scrollbar even if the the content falls within the dimension of the ScrollViewer

<Canvas x:Name="can">
    <ScrollViewer Width="200" Height="200"
                  Canvas.Left="30" Canvas.Top="30">
        <TextBlock Text="Lorem Ipsum Lorem">             
        </TextBlock>
    </ScrollViewer>
</Canvas>

In order to prevent a vertical scrollbar to be displayed, just set the VerticalScrollBarVisibility property to Auto

<Canvas x:Name="can">
    <ScrollViewer Width="200" Height="200"
                  Canvas.Left="30" Canvas.Top="30"
                  VerticalScrollBarVisibility="Auto">
        <TextBlock Text="Lorem Ipsum Lorem">             
        </TextBlock>
    </ScrollViewer>
</Canvas>

The Vertical ScrollBar does not appear now.