Hey Francis.
The simplest way is to upload the product files in some location online. Somewhere like Dropbox or Google Drive.
You can then use email automation software which will automatically send the email which will have the link of the product from which the buyer can download it.
You need to do some set-up at the back-end within the email automation software where, when someone buys your product, they get added to an email list in your email automation software. Once they are successfully added, they are automatically sent the email with link to download the product.
If you have any question, feel free to ask.
Umair
https://salesfunnelri.com/resources/