This article illustrate how to open a PDF from a specific page.

You need to Open the PDF and after a delay call the PDFGotoPage to go to the page you want! The delay allows the PDF to open properly and go to page when the PDF is ready.

m_reader.PDFOpen(m_doc, false, this);
new Handler().postDelayed(new Runnable() {            
    public void run() {
        m_reader.PDFGotoPage(pageToGo);
    }
}, 100);