PDF Viewer supports the using the keyboard to navigate and interact with various interfaces throughout the app.
To get a list a of all the shortcuts available at any given time, press and hold the Command (⌘) key on your keyboard.
The following screen displaying the available shortcuts will pop up:
Using Escape on the Apple Smart Keyboard
The Apple Smart Keyboard does not have a physical Escape key. On these keyboards, you can input escape using ⌘ . (Command - Period).