A: The master file is stored on the server with permissions restricting read/write/execute rights over http protocol. Upon the sale, temporary copy of the file is created on the server with read over http permissions. It is uniquely named and is available for the download though the (again) unique link. This link can be accessed only limited number of times (such as 1 time). After one successful download the temporary copy of the file is deleted from the server or read permissions are changed.