Choose View > Navigation Panels and select the desired panel (Comments and Pages).
Click 
at the bottom of the vertical bar that separates the Document Panel from the Navigation Panel, to show/hide the Navigation Panel.
The Navigation Panel can display the following:
When you select a panel, it gives you access to a set of tools related to the current display.
To show or hide the Navigation Panel
Choose View > Navigation Panels and select the desired panel (Comments and Pages).
Click at the bottom of the vertical bar that separates the Document Panel from the Navigation Panel, to show/hide the Navigation Panel.