As more software functions move to the Internet, where the traditional software licensing business model has limitations, companies are experimenting with new business models such as subscriptions and advertising-supported software.

Microsoft is trying it with its Works suite, which comes standard -- and free to the user -- on many new computers. Likewise, Google Docs and Spreadsheets -- online versions of the productivity apps dominated by Microsoft -- are advertising supported. Now Adobe, a leader in rich Internet applications with its Flash player and nearly ubiquitous PDF reader and writer, is getting into the act with help from Yahoo.

On Thursday, the companies announced a partnership to allow publishers to serve contextual ads into PDF documents. Like all of these early ad-funded software efforts, this is a test program for starters and it's opt-in.

From the release: "The new service allows publishers to generate revenue by including contextual, text-based ads next to Adobe PDF content, with Yahoo! providing access to its extensive network of advertisers to match a broad range of subject matter. For advertisers, Ads for Adobe PDF Powered by Yahoo! extends reach by delivering advertising across a new channel of content, while also providing the ability to track advertising performance, just as they can today with ads placed on Web sites."

This in-PDF advertising seems clearly targeted at the long tail of the Internet, as this excerpt from AdWeek's coverage of the news illustrates:

The program will open up new real estate for its advertisers, according to Todd Teresi, svp of Yahoo!'s publisher network, especially among small-time customers that don't even have Web sites. Example: Local youth soccer leagues that create weekly e-mail newsletters could generate funds through contextual placements for soccer equipment and jerseys -- and even minivans, he said.

"The primary users long term are going to be down the tail," Teresi said.

The program is offered as a free service to US-based publishers who produce English content. Early adopters include IDG InfoWorld, Wired, Pearson's Education, Meredith Corporation and Reed Elsevier.