Software maker Adobe Systems Inc and Internet company Yahoo Inc said on Wednesday they will offer a service to let publishers run advertisements in Adobe's popular document-reading format.

The new service, Ads for Adobe PDF Powered by Yahoo, presents publishers with an alternative to conventional subscriptions, which, if widely adopted, could open up a new model based on free, ad-supported publishing, analysts said.

Advertisers gain a distribution channel that can reach highly specific audiences based on their reading interests while allowing them to track how specific ads perform. The approach is akin to how Web-based, pay-per-click ads now work.

The text-based ads are displayed in a panel adjacent to the content with no moving or flashing elements. Each time the PDF is viewed, ads are matched by Yahoo to the content.

In terms of relevance to advertisers, such ads could rank above Web-page banner ads in terms of targeting capacity, but below specific keyword-based Web ads, Teresi said.