I can't figure out how to move a screen full at a time through an issue.

I am using Windows.  I installed the DVDs.  I can launch the navigator application.  I can open issues.  I can make the issues full screen.

What I can't figure out how to do is scroll through a screen at a time.

If I do the down arrow key, it moves a few lines.  If I do the page down key, it jumps to the same position on the next page in the issue.  What I want to do is just move down a screen full.  Even the scroll bar does work right with the mouse: if I click in the area below the thumb, instead of moving a screen full, it acts like the down arrow key, and for that matter, the arrows in the scroll bar.

This makes it really hard to read articles.