You can use K2Store to sell digital goods. The K2 attachments are treated as the digital goods here. You can set it in a few steps.
1. Create a K2 Item
2. Upload your file(s) via K2 Attachments tab.
3. Enter the price in K2 Store block.
Now you have set up the Digital Item for sale.
After the purchase, the customer needs a place to download. So create a menu.
1. Go to Menu and choose K2Store as the Type.
2. Then choose Downloads view.
3. Set the access level to Registered. IMPORTANT NOTE: Guest users cannot download the attachments. The attachments will be emailed to them.
Video tutorials about this feature will be made available soon.