Here is the problem I'm confronting. I am making a considerable number of various PDF files available for download, but some are being widely pirated. What I would like to do is to have some way of automatically and invisibly watermarking the file with the ID of the downloader. All the downloads are done through my site so the user has to sign up first and has a unique user name. So what I would like to have automatically written either in the metadata or somewhere else in the file where it is invisible to the general reader the following:
Downloaded from xyz.com by toupie098
If we could expand this to be:
Downloaded from xyz.com by toupie098 from IP 126.96.36.199 on 12/12/2014 at 20:47 UTC
That would be even better, but the first option would be fine.
I'm aware that just writing it in the metadata is relatively easy to find and to erase, but I've been reading about different ways to do so in the Dictionary, etc. The important aspect is that the entire process be automated as I wouldn't be able to integrate a manual process for each download. Thank you in advance for your assistance.
You can't use Adobe Acrobat for this. Look for a server product.