Restricting those that can complete a form

It is possible to restrict who is able to compete a form? Typically I would include the form link in an email to the target audience. What we are trying to avoid is anyone sharing this link with others that are not part of the intended audience. 

Thanks, 

Emily 

There is no way to truly prevent someone from filing out a form.  It is possible to do things like hide the form contents unless the form is visited from a specific URL or somewhat password protect the form, but in both instances that information could be shared.