Adobe and Yahoo are bringing advertising to electronic documents.

The two companies plan on Thursday to announce Ads for Adobe PDF Powered by Yahoo, a new service for publishers interested in generating ad revenue from their digital content.

The opt-in service will be available initially as a limited beta test, open only to select partners including IDG InfoWorld, Wired, Pearson's Education, Meredith Corp., and Reed Elsevier. Neither Adobe nor Yahoo has committed to a date for general availability.

But eventually anyone with an Adobe account and a Yahoo Publisher Network account will be able to participate.

Publishers first upload PDF files to Adobe. Once digital content gets associated with the publisher for purposes of payment, it gets analyzed so that Yahoo knows what type of ads to place in the document. The files then get ad-enabled and e-mailed back to the publisher to be distributed as the publisher chooses. Thereafter, when opened, ad-enabled documents will call out to Yahoo to fetch dynamic ads for display, provided the PDFs are being read on an Internet-connected device.

As with ads on Web pages, publishers get paid per valid click.

The ads will appear in a sidebar, without altering the layout of the content beyond the addition of the sidebar.

"We really wanted to make sure that the ads can be viewed without getting in the way of the content and people could still have a great user experience in terms of interacting with the content," said Kurt Garbe, entrepreneur-in-residence in advertising at Adobe.

Readers of ad-enabled PDFs will be able to close the side panel that displays ads or to disallow PDFs to connect to the Internet when prompted with a network connection dialog -- a wise security precaution.

"The advertisers are really excited by this because it provides a whole new set of inventory out there," said Garbe.

He also expects that the service will help publishers experiment with new business and pricing models for content. Said Garbe, "I don't know how much this is going to change publishing so much as recognize that it's changing anyway."