Microsoft has been granted a patent on 'Page Up' and 'Page Down' keystrokes.
The software giant applied for the patent in 2005, and was granted it on August 19, 2008. US patent number 7,415,666 describes "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".
The patent's listed 'inventors' are Timothy Sellers, Heather Grantham and Joshua Dersch. However, Page Up and Page Down keyboard buttons have been in existence for at least quarter of a century, as evidenced by this image of a 1981 IBM PC keyboard.