> Product documentation is also available to prospective customers so they can review it to decide whether they want to purchase the product.
I agree with this statement, but it is irrelevant. The primary purpose of documentation is what I said: for understanding how to operate the product. The only purpose of advertising is to make a sale. Advertising has no secondary purpose. These are not the same thing.
The test is quite simple: Is the sole purpose of the payment to make a sale? If so, it is advertising.
We don't really need to discuss documents any longer. Documentation is not an advertisement.