To create a PDF portfolio containing multiple file types.

void addPackage(PDFDoc doc, String file, String desc) throws PDFNetException {
	NameTree files = NameTree.create(doc.getSDFDoc(), "EmbeddedFiles");
	FileSpec fs = FileSpec.create(doc, file, true);
	files.put(file.getBytes(), fs.getSDFObj());
	fs.getSDFObj().putText("Desc", desc);

	Obj collection = doc.getRoot().findObj("Collection");
	if (collection == null) collection = doc.getRoot().putDict("Collection");

	// You could here manipulate any entry in the Collection dictionary.
	// For example, the following line sets the tile mode for initial view mode
	// Please refer to section '2.3.5 Collections' in PDF Reference for details.
	collection.putName("View", "T");
}
PDFDoc doc = new PDFDoc();
AddPackage(doc, filename, "PDF");
AddPackage(doc, imagename, "Image");

PDF packages (portfolios)
Full code sample which illustrates how to create, extract, and manipulate PDF Packages (also known as PDF Portfolios).