This event is useful, for example, to update a "current page number" display in your application.
The page change event is called whenever the displayed page number changes. This can happen in several ways:
- the user hits the Page Up or Page Down key
- the user clicks on a hyperlink to a different page (or different PDF file)
- any of the "goto" or "scroll" functions are called
In continuous mode, this event is triggered when the page displayed in
the middle of the window (i.e., at the vertical center of the window)
pageChange for an event triggered when the page at
the top of the window changes.