Why conference chair asks for accepted papers sources?
While we obviously do not know the Chair's intent (unless she happens to be a stack exchange poster), the most likely situation to me is that there's some sort of formatting related issue (or possibly some typos, etc. that need correcting) in your submitted version that they are incapable of fixing given your PDF file.

This does not necessarily imply it's your fault - typesetting systems are sometimes fussy, but asking for both a Word version and the source indicates, to me, that they want "A version they can edit".&nbsp;&nbsp;&nbsp;

On a practical level, yes, it's your problem. You could refuse of course, with unknown results.