It was just a matter of time before paid search bumped up against the PDF.

Yahoo! (NASDAQ:YHOO) is teaming up with Adobe (NASDAQ:ADBE) to serve contextual market ads as readers scroll through Web-published pages in Adobe's popular PDF platform. Relevant ads appear to the right of the actual document within Adobe's Acrobat or the free Adobe Reader programs.

The pair has a history, having partnered a few years ago to offer tools for Acrobat. And this is a great move, especially since the publishers get to decide whether they want to monetize their PDF files this way.

Sure, publishers can sell ads on their own. Instead of having to split ad revenue with both Yahoo! and Adobe, they could seek willing sponsors, charge accordingly, and pocket everything. However, Yahoo!'s system serves up a column of dynamically targeted text ads, seamlessly tracking performance and payout information.

Few small and home-based newsletter writers can afford that kind of operation. Heck, even the big boys can't compete with the amount of names Yahoo! has in its list of contacts. Publishers such as Meredith (NYSE:MDP), Reed Elsevier (NYSE:RUK), and Pearson (NYSE:PSO) have been willing guinea pigs in the new program's beta, awkwardly titled "Ads for Adobe PDF Powered by Yahoo!" It's a mouthful for a handful, isn't it?

We always knew that contextual marketing would be more than just a search-engine staple. Yahoo!, Google (NASDAQ:GOOG), and Microsoft (NASDAQ:MSFT) have spent way too much time growing their ad networks to settle for the low-lying fruit in their own backyards. Whether it's Yahoo! building a consortium of hundreds of newspapers or Google dabbling in print, television, and radio advertising, if the approach is incremental, they're going to find a way to exploit their relationships.

Are ads distracting to readers? You bet. Do they pay the bills behind a lot of the free content available in cyberspace? You'd better believe it. Will we ever get to the point where contextual marketing becomes so ubiquitous that ad blindness will kick in? Will unclicked ads therefore be rendered worthless, unless they're billed by the number of impressions rather than clicks? For the sake of the paid-search stars, let's hope not.

For related Foolishness:

Yahoo! has been recommended to Stock Advisor subscribers. Microsoft is an Inside Value selection. Why are you missing out on these great stock picks? The answer may be waiting in free 30-day passes to any or all of the newsletter services.

Longtime Fool contributor Rick Munarriz isn't one to complain about ads on the margin of PDF files. Then again, he doesn't complain much in general. He does not own shares in any of the companies in this story. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.