At this stage, I'd suggest your client try opening the document(s) on another computer with the same regional & language settings. If the document(s) display correctly there, the problem may be with the Windows installation itself. In that case, try running:
SFC /scannow
from a command prompt with Admin priviledges.

If that doesn't resolve things, and the errant PC worked OK previously, restoring the OS to a date when it did work, using System Restore, may suffice. If that doesn't apply or otherwise resolve things, a complete uninstall of Office (see Option 2 at: https://support.office.com/en-us/art...c-2fdf5dbf61d8), followed by a reinstall may be called for. And, if that doesn't work, a repair install of Windows 10 may be required. See: https://www.tenforums.com/tutorials/...e-upgrade.html

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]