Can my forms be changed by the person completing the form?

The forms cannot be changed by persons who are simply filling up the form, unless the person is a sub-user which you have assigned under your account. You can check this guide to know more about sub users: https://www.jotform.com/help/232-How-to-Share-Forms-with-a-Sub-account-User

Or, if you have given someone a link to do collaboration to your form that you are creating. Please check this guide for more information about form collaboration: https://www.jotform.com/help/419-Understanding-Form-Collaboration

If you believe that your form was modified, you may check your form's revision history. Please check this guide to know how: https://www.jotform.com/help/294-How-to-View-Form-Revision-History

Thanks.