Suppose a company wants to write some product documentation so customers and prospective customers know what features their product has and how to use them. They hire someone to write the documentation and then someone else to distribute it. Is there a good way to distinguish this from advertising?

The most plausible way would be if the one you're paying to distribute it has some kind of exclusive control or market power over the distribution channel so that you're paying them a premium over competing distributors. But then wouldn't the best way to prevent them from extracting that premium to be to make it so nobody has exclusive control over distribution channels, e.g. by breaking up concentrated markets or requiring federated protocols?