Hello Mark,
I looked into this for you, and there does not seem to be a "built-in" solution for this in Prestashop. There is a post in the Official PrestaShop forums, where they are working on a possible solution.
You can also purchase a module for accomplishing this, such as Virtual products management.
Aside from these solutions, you may be able to find a developer that can custom code this functionality for you.
If you have any further questions, feel free to post them below.
Thank you,
-John-Paul
Hello pryanwise,
Thank you for your question. First I recommend following this guide on creating downloadable products in prestashop.
After it is added, you would treat it as a normal product in prestashop, just make sure that the file downloads are enabled. Here is a guide on enabling downloads that I found via google search.
We also have a full Prestashop education channel, that includes video tutorials, and guides on using Prestashop.
If you have any further questions, feel free to post them below.
Thank you,
-John-Paul