Adobe ACROBAT READER 7.0 Manual page 181

Scrolling automatically
The automatic scrolling feature makes it easier to scan through long PDF documents,
especially reflowed documents. You can scroll through pages without using keystrokes or
mouse actions.
To scroll automatically through a document:
1. Choose View > Automatically Scroll.
2. Do any of the following:
To change the scrolling speed, press a number key (9 is the fastest, and 0 is the slowest),
or press the Up or Down arrow keys.
To reverse the direction of the scrolling, press the hyphen or minus sign key.
To jump to the next or previous page, press the Left Arrow or Right Arrow key.
To stop automatic scrolling, press Esc or choose View > Automatically Scroll again.