Fair enough that it isn't steganography, though it can be used for similar applications. Do "Most viewers" show it? Google Chrome doesn't, nor does Preview on

Fair enough that it isn't steganography, though it can be used for similar applications. Do "Most viewers" show it? Google Chrome doesn't, nor does Preview on a Mac. There is no easy way to add attachments to a PDF, except Adobe Acrobat Pro or iTextPDF. Firefox and Adobe Reader can read the attachments, but it's "hidden" to some degree, inside slide-out side menus. Certainly enough to avoid a casual glance.