Save form data to local machine for reuse

I have a php form that generates a work procedure for configuring routers. The form has about 20 fields. The process can span a couple of days and there can be a few configs going at the same time. I'm looking for a way to save the form data to the users machine and then have the ability to reopen the webpage and fill in the form with the locally stored data. I can use a save file /load file button, but ideally it would be great to have a "save" button that allows user to save a html (or other file that is associated with web browsers) that contains the completed form data. To load the "completed form", the users clicks the saved file and the web page opens with the form already filled in.