Besides, if they need to "edit" they can annotate ad mark up a PDF and then submit it back to you for recommended changes. If they need to add something ahead of your resume they should include another cover sheet or again, annotate the top of the PDF with their own watermark perhaps. This would look far more professional for them and the people who created the original resumes.

The only people that should be getting source files (original editable documents) are people in a production/print industry involved with producing final output documents for you. No one in that industry wants to see a Word document, but that's besides the point.