How to store a single page as byte to store in a database?
Assuming the PDFDoc object contains other pages, then something like the following would isolate that one page and give you back the bytes for it.
// 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();
ArrayList imported = sink.ImportPages(importList, importBookmarks); // where importBookmarks is a boolean. Set to true if you care about preserving bookmarks
sink.PagePushBack(imported as Page);
byte pdfPageData = sink.Save(SDFDoc.SaveOptions.e_remove_unused);