The number of patents that Microsoft has is closing in on the 10000 mark, up from “only” 5000 in 2006. Added to this venerable list is the application made in 2005 for Page Up/Page Down functionality. This patent was granted to them on the 19th of August 2008. This is almost as funny as their patent for double clicking and for a mouse wheel for scrolling.

Excerpt

A method and system in a document viewer for scrolling a substantially exact increment in a document, such as one page, regardless of whether the zoom is such that some, all or one page is currently being viewed. In one implementation, pressing a Page Down or Page Up keyboard key/button allows a user to begin at any starting vertical location within a page, and navigate to that same location on the next or previous page. For example, if a user is viewing a page starting in a viewing area from the middle of that page and ending at the bottom, a Page Down command will cause the next page to be shown in the viewing area starting at the middle of the next page and ending at the bottom of the next page. Similar behavior occurs when there is more than one column of pages being displayed in a row.