// given x is the page you want to store (index starts at one)
// given source is PDFDoc containing page x
PDFDoc sink = new PDFDoc();
ArrayList importList = new ArrayList();
importList.Add(souce.GetPage(x));
ArrayList imported = sink.ImportPages(importList, importBookmarks); // where importBookmarks is a boolean. Set to true if you care about preserving bookmarks
sink.PagePushBack(imported[0] as Page);
byte[] pdfPageData = sink.Save(SDFDoc.SaveOptions.e_remove_unused);