A PDF file is a file. Anyone can copy any file, any time, e-mail it,
put it on a disk or an iPod, without limits. They can do this whether
or not Adobe Reader is installed on a computer, just by dragging and
dropping the files or whatever.
So, I can see that you might see this as a simpler way of protecting
files, but in fact it's just impossible. What IS technically possible
is solutions which tie a PDF file to a particular machine or user, so
that the copy is useless to anyone else - which is back to DRM.
PDF security, such as it is, is based on DRM solutions, which by their
very nature tend to be a bit high end. For example, they tend to need
a server 24/7 on the internet to keep track of who is allowed what.
Nolos_Retep's proposal is technically possible but would require a DRM
plug-in to be written for Reader. This makes it much more expensive
than most commercial solutions, the DRM plug-in license costing tens
of thousands of dollars. It would also need custom server software.
However, it has some similarities to products from FileOpen, so take a
look at them.
Aandi Inston