Placid writes to alert us to a new channel opening up between advertisers and our eyeballs: PDFs with context-sensitive text ads. The service is called "Ads for Adobe PDF Powered by Yahoo" and it goes into public beta today. The "ad-enabled" PDFs are served off of Adobe's servers. The article mentions viewing them in Acrobat or Reader but doesn't mention what happens when a non-Adobe PDF reader is used. The ads don't appear if the PDF is printed.