We're trying to validate legal professionals as a segment via AdWords for our app that synchronises document viewing across multiple iPads. (no need for projector or hanging over shoulders, it also works remotely via VoIP).
The only AdWords keywords that will perform well on search are ones that directly describe your product, e.g. "document syncing." To target a segment like legal professionals, use AdWords' Contextual Targeting Tool to build ad groups to target websites that your target market would visit, e.g. anything related to law.