The controls are easy to use! From left to right:

+ or - makes the image larger or smaller.
Click the grid symbol to show page navigation on the left of the screen.
Click the printer icon to print the document, and click the arrow pointing down to download it.
Click the broken square to see the document full-screen (when viewing in full-screen mode, the symbol will turn to a broken cross symbol – click to return to standard view).
Click the magnifying glass to search the document, and click the curvy arrow to forward it to someone else.