Three different members of Adobe Support have unfortunately been unable to resolve this problem so I am pinning all of my hopes on my fellow users! Please Help!
I have been sent a PDF by my client (created via their previous agency) which when opened in Reader (not Acrobat) enables me to edit the existing text (in the existing fonts, granted only Helvetica) and re-save it as a hi-res PDF.
I have tried virtually everything to get this to work without success, I can create 'editable fields' but this deletes the existing text and inserts a blank box over the top which I can type into with the default 'Times'.
What will ultimately happen is that I will design the documents in English and then they will be uploaded to an ftp for download at various offices around the world. Therefore they need to translate what we have written but retain the same document design.
I know this is possible because I have the PDF in front of me, I also know that PDFs in essence weren't designed to be editable but apparently it is now achievable and very useful if I can get the blasted thing to work 
Very many thanks, your opinions will be most appreciated!
Regards
Adamskidog