I don’t use a PC so I don’t know if this applies to PC’s (but then again, I don’t think a PC user would be on this blog), but there is a very quick shortcut for “Page Down”.
Tap the space bar to move one page down, equivalent to hitting the “Page Down” button. And like many other shortcuts, Shift + Spacebar is the opposite of pressing the space bar, and is the equivalent of the “Page Up” button.
