The Preview Canvas
can be split into two, either
horizontally or vertically, offering two independent views of the
document. The second, assistant, view cannot be used for editing
operations, but it can be useful for reference while reading or
working with the default view. The contextual menu on the assistant
view (the view on the right) offers a Go to Page
menu for quick
navigation. Alternatively, having the [Alt] key down while clicking in
the page list or the outline list will navigate both the main and the
assistant view to the selected page.
To show the assistant view, select the appropriate option from the
View->Split
menu.