This would usually only happen if the originals were .doc, .dot, .docm, .dotx or .dotm files and someone changed their extensions. Does your Office installation open docx files created in Word 2013? If not, perhaps the Office installation is
faulty. In that case, try repairing the Office installation (via Programs & Features > Microsoft Office > Change in the Windows Control Panel).
Cheers
Paul Edstein
[MS MVP - Word]