AFAIK the worst at compatibility is Word 2011 for Mac. It wasn't difficult for example to find Mac Word 5.1 documents that open perfectly fine in Word 2010 for

AFAIK the worst at compatibility is Word 2011 for Mac. It wasn't difficult for example to find Mac Word 5.1 documents that open perfectly fine in Word 2010 for Windows (after unblocking the file format) which would display nothing but garbage when opened in Word 2011 for Mac.