How do I address font issues on the client's end?

Hi all,

We are working on an assignment where we are converting Arabic PDFs to Word. 

Our linguist is expected to deliver an error free document, to the last period and comma - basically a carbon copy of the PDF document into word. The client would change this word document into ePub format.

The issue we are facing here seems font based.Vowel marks are disappearing and the client doesn't seem to understand that changing the settings is what is required. His UAE based client says this "Settings" issue is not agreeable. 

How do we make sure that the client gets the document and converts it into an ePub without errors?

Please help. Grateful in advance.