Hope all is well with you.
I suggest to give a try to this app https://apps.shopify.com/digital-downloads
I guess it can help you with your requirement. If this is not what you are looking for then you may need a custom app where you can set the download link and licence key correspond to the products and whenever any order is placed app will send the related details to the user right away.
let me know it you need more information on this.