It is no secret that you can sell almost anything online these days if you have a PayPal account. Thanks to PayPal Green Downloads plugin, you can sell files on your site. It generates encrypted download links that are valid for a limited time. You can even host files in Amazon S3 buckets to grant temporary access to them.
The PayPal Green Downloads plugin allows for free downloads. It also keeps track of button impressions, payments, and downloads. You can embed buttons into 3rd party sites and export all your download links in CSV format.
The PayPal Green Downloads plugin also takes care of email notifications. You can find out more here.