We have a WordPress project where the client wants to do the following: users upload a “conversation” consisting of an audio file and a PDF, and the uploader sets a price they want to sell it at. Then other users can purchase, listen & view the page contents (the audio and PDF) online. It could be a WooCommerce product unless you recommend some other e-commerce system. I've already created a Custom Post Type with custom fields for this purpose, but I'm not married to it.
Conversation product will be downloadable product. Woocommerace along with dokan has downloadable feature. You can also attach a PDF file in that product for download. Can you please check our demo in this link – http://demo.wedevs.com/dokan.
What I meant was, the most important part of my original question was about the user – site visitors – being able to create a product from the front end. They upload an audio and PDF, and set a price.
Secondarily, it's not a downloadable product, it's to be viewed in the page after purchasing.