title: Detecting a PDF Package or Portfolio in code
body: <p>Does anyone know of a way to detect whether a given PDF file is a PDF Portfolio or a PDF Package, rather than a "regular" PDF? I'd prefer Java solutions, although since I haven't yet found <em>any</em> information on detecting the specific type of PDF, I'll take what I can get and they try to figure out the Java solution afterwards.</p>
  
  <p>(In searching past questions, it appears that a bunch of folks don't know that such things as PDF Portfolios and PDF Packages exist. Generally, they're both ways that Adobe allows multiple, discrete PDFs to be packaged into a single PDF file. Opening a PDF Package in Reader shows the user a list of the embedded PDFs and allows further viewing from there. PDF Portfolios appear to be a bit more complicated -- they also include Flash-based browser for the embedded files, and then allow users to extract the discrete PDFs from there. My issue with them, and the reason I'd like to be able to detect them in code, is because OS X's built-in Preview.app can't read these files -- so I'd like to at least warn users of a web app of mine that uploading them can lead to diminished compatibility across platforms.)</p>