Advanced Product Attachments (M2) - Add Attachments to Orders
Add Attachments To Orders
You can enable or disable this feature in Advanced Product Attachments (M2) - Configuration
Once you allow adding attachments to orders, customers can find all attachments regarding completed orders in their accounts in the My Orders section.
All the necessary files are stored in Items Ordered in the customer account. Each order can have a separate set of files. The customer can view or download the files from that section.