Unable to open any PDFs in a directory after a restore of files from backup

Hello,

A user deleted an entire directory (and all subdirectories) of PDFs.  When they were restored, none of the PDFs can be opened using Acrobat Reader.  I have even tried other PDF readers.  None have worked.  Is there a setting that I am missing or a utility that I can run to fix this?  We are talking about 100s of files that were restored but can not be opened.  We have tried to run PDFFix Toolbox and others.  Nothing seems to work.

Thank you!