Making an editable PDF for mobile devices secure

[grahamn97422988]

Hello! Hoping someone will be able to help... 

We have some editable forms (created in Indesign and exported to PDF) for a client where the content must be 'secure' by means of a password but still editable for the user. So for example, copying content is locked but filling of form fields is unlocked.

For desktop devices, this works as it should, however, when viewed on Android and iOS devices, the filling of form fields no longer work. I've tried different settings and acrobat versions, but every single time, the fields are no longer editable unless the PDF is 'unsecure' which is just not an option for our client. 

Has anyone come across this or know of a solution that we can implement?

Thanks