PDF Packages were introduced in Acrobat 8.0 and they themselves were an extension to simple file attachments in a PDF file. With PDF Packages, you could combine multiple PDF files into a single “Package” with each file remaining a discrete entity with it’s own security settings but you could also combine Dynamic XFA Forms and static PDF Forms (Acroforms). What distinguished PDF Packages from ZIP files is that you could add descriptive text and metadata in context and you’d get a little thumbnail to help you find the specific files you wanted across the whole set.