HP ePrint is a free application with which you can print documents that is in the Inbox, emails sent to Printer. In order to access HP ePrint remotely, You should enable the Web Services on your Printer.
Note: You can Sign up in 123 HP Envy 4520 Connected to create an account. Using the Log In credentials and view HP ePrint job status, manage your HP ePrint printer queue etc,. You can also download and install the Free product update from your account.