You're not showing the code you currently are using, but your problem likely stems from the fact that you don't realize there is an additional layer present here. The document methods in the Adobe PDF library truly only deal with the PDF file itself and a PDF file doesn't have a current page number.
To display PDF documents, Acrobat uses an AVPageView. The AVPageView is your link for anything that concerns the display of your PDF files.
AVPageView has a method to get the currently visible page:
PDPageNumber AVPageViewGetPageNum(AVPageView pageView)
So from the document, get its page view and work with that to get the page number, zoom factor, display mode and so on.