Adobe displays contextually relevant ads in the sidebar when your PDF files are viewed inside Acrobat Reader (see screenshot) – you make money based on clicks just like Google AdSense.
Today, Adobe announced certain changes that makes the program all the more tempting.
For instance, publishers can now embed ads inline with the content rather than displaying ads in the sidebar which often go unnoticed. See AdSense heatmap.
Other than deciding the location of Yahoo! ads in the PDF files, you also have the option to change fonts and color schemes so that the ads blend more nicely with your content and thus yield better CTR.
Tempting, right? The issue is that Adobe Ads for PDF program uses Yahoo! ad inventory and is only available for US based publishers since you require an SSN at the time of signing up.
Google has a much larger pool of advertisers than Yahoo! and can serve highly relevant contextual advertising but they generally limit themselves to displaying ads only on web pages. So am not sure if Google would agree to partner here but Adobe should seriously consider accepting international publishers.