You can create a downloadable product and the customer will be able to download any file or files after the purchase.
Note! You can sell downloadable products only to registered clients (not in Guest checkout)
Go to Catalog - Downloads and Press "+ button" to upload a file
2.1 Go to Catalog - Products and Press Press "pencil button" to edit or "+ button" in top right corner to create a new product
2.2 Press Advanced settings link in the Organization block
2.3 Add files you want to sell in Downloadable files section (start typing file name)
2.4 Save button in top right corner
After the purchase, the client will see the order confirmation information with the link to the files. This link will also be attached to the order confirmation email.
Note! Order status should be Confirmed, otherwise, the client will not see the files.