To create a PDF portfolio containing multiple file types.

func AddPackage(doc PDFDoc, file string, desc string){
	files := NameTreeCreate(doc.GetSDFDoc(), "EmbeddedFiles")
	fs := FileSpecCreate(doc.GetSDFDoc(), file, true)
	key := make([]byte, len(file))
	for i := 0; i < len(file); i++{
			key[i] = file[i]
			//fmt.Println(file[i])
	}
	files.Put(&key[0], len(key), fs.GetSDFObj())
	fs.SetDesc(desc)

	collection := doc.GetRoot().FindObj("Collection")
	if collection.GetMp_obj().Swigcptr() == 0{
			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");
}
doc := NewPDFDoc()
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).