To create a PDF portfolio containing multiple file types.

void AddPackage(PDFDoc doc, string file, string desc)
{
	NameTree files = NameTree.Create(doc, "EmbeddedFiles");
	FileSpec fs = FileSpec.Create(doc, file, true);
	byte[] file1_name = System.Text.Encoding.UTF8.GetBytes(file);
	files.Put(file1_name, fs.GetSDFObj());
	fs.GetSDFObj().PutText("Desc", desc);

	Obj collection = doc.GetRoot().FindObj("Collection");
	if (collection == null) collection = doc.GetRoot().PutDict("Collection");

	// 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).