To navigate a PDF file page-by-page, use the Page Controls options on the bar at the bottom of the window:
TIP: You can also use Page up and Page down keys to scroll, as well as the left and right arrow key to jump to the next or previous page.
Click and slide the scroll bar on the right side of the document pane to gradually scroll through pages of the document.
TIP: You can also use the up or down arrow keys, or the scroll wheel on your mouse to scroll smoothly through pages in a PDF document.