Password protecting fillable forms.

I have created a form in InDesign and then exported as Interactive PDF. I have 'locked it down' with a password to stop anyone with full Acrobat editing it. I need different people to complete parts of the form, so I have then made it Reader Extended. Ideally I want people with just Acrobat Reader to be able to password protect the form before mailing it onwards. Can we do that? How? Thanks!