Remove 'edit' function once a completed form is saved (Adobe InDesign)

Hi folks, 

I've created an 'interactive' form using InDesign which provides drop down boxes etc.

When I ask someone to fill the form in, and they send it back to me, all the fields are still 'editable'. 

I was just wondering if there was a way I could set up the form, so that as soon as someone completes the form and clicks 'save as' then the edit function can be removed? This is more so to prevent me (or others) from accidently amending a form. Any guidance would be great! Thanks in advance.