User can not edit a PDF form after updgrading her device

Hi,

I have upgraded a user from a Surface Pro 3 to a Surface Pro Book.

She can no longer edit fields on some PDFs forms.

As an example, if she has two files originating from the same PDF,

   one called:   'Document draft.pdf'

   and another called:   'Document final.pdf'

she can edit the 'draft' version but not the 'final'.

I have noticed that the 'final' version is signed.

Can anyone suggest how I can allow her to edit all of her PDF files?