My friend uses Windows 7. She has an 8GB generic USB flash drive formatted MS-DOS Fat32 with around 4GB of Word (.doc and .docx) and PDF (.pdf) files on it. The drive mounts fine. All of the files look OK. They can be copied, renamed, etc. But every single file, whether opened from the original flash drive or from a hard drive they've been copied to, says it is corrupt and cannot be opened. I've tried opening from the flash drive and from a hard drive copy using Win 7 Pro, Win 10 Pro, OS X Yosemite and OS X El Capitan, with various versions of Microsoft Office, OpenOffice, Adobe Reader, and Adobe Acrobat. Any thoughts?