I am glad you found the source of the issue for the image uploader. Do you mind sharing which plugin was the culprit?
As for your question…
If you list the product as a DOWNLOAD product type, you fill in the fields with the product file, and when the buyer purchases the product, they are provided with a download link that will “deliver” the digital product. This is also true with the Virtual product type.
Is there something more of different you are needing for the delivery of digital products?