Posted each time a write operation begins working on a page in a document.
The notification object is the PDFDocument object itself. To determine the page, use the @"PDFDocumentPageIndex" key to obtain userinfo of type NSNumber.
Available in Mac OS X v10.4 and later.
Declaration Syntax Version Information- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)