4thePegeh... if they are hotlinking PDFs in the same window you can take the hit and redirect it to a landing page on your site totally 'stealing' the traffic. If you create the pages right the person might not even realize they were on another site.
We had a situation like this, I have told this story on here before but, this lady was selling the same products as I for this one site.
I had taken the time to make up really nice PDFs with product shots and descriptions, she decided that they were so nice that she would use them too... but she didn't even copy them to her server, she just linked mine and in the same window.
I noticed this so I wrote a rewrite rule and sent those hits to an .html page that had the product info and pictures and had a "Buy" link... I got about 50 sales from her site before I got an email from her.... the email said..... Your PDFs are broken, can you fix them..... it was quite panicky so I decided she had suffered enough and explained what was happening.
She didn't even understand what she had done and was some girl out of school this place had hired to do content.
But for images and stuff I have made custom images to replace hot-linked images that say
"Visit www.example.com to see more"
'Stolen content... come to example.com for real info'
[edited by: Demaestro at 5:26 pm (utc) on July 7, 2008]