PDF2XL allows for some customization of the user interface. For example, you can choose to show or hide the Pages and Preview panes by using the toggle buttons on the View tab.
You can also change the position of the Preview pane using a drag and drop method.
Just for clarification, the Preview pane is the bottom screen in the default view:
Step-by Step Instructions
Left-click and hold with your mouse on the Preview pane toolbar.
While holding the mouse button, drag the pane away from its locked position.
Once you start moving the pane, you'll see a quarter-arrow button appear on the screen - place your cursor over the position you want and release the mouse button to lock the pane in place.