PubMatic stock tumbled after the company's guidance fell short. Shares of adtech company PubMatic (PUBM -21.14%) took a beating on Tuesday following a second-quarter report that was mostly positive, save for one piece of bad news. The stock was down more than 20% in morning trading. Is this rout an opportunity to pick up shares of PubMatic at a knocked-down price? Or should investors steer clear? Plenty of good news PubMatic, which operates a supply side platform that helps publishers and app developers mon ...