Unable to use protected pasword fillable form eben when set up correct permissions

i created a fillable form, i need to share with customers so they fill and send back, but i dont want anyone able to edit the backgorund or fields, i pasword protected, only to edit pages, i left permissions for access contenct, text and forms, but on iphone it wont let to use the fillable fields, the pasword protected message comes all the time, and user is unable to even write on the fields, this was te purpose of the form, any help i cannot share the password with every customer neither can i send the form open so anyone can replicate it or steal it. need help asap please