Trying to open word document throws InvalidDataException

I'm trying to open a .doc file using OpenXML and I am getting the following error:

System.IO.InvalidDataException: 'Number of entries expected in End Of Central Directory does not correspond to number of entries in Central Directory.'

My code is really simple...

var filePath = "C:\\[Rest-Of-Path]\\file.doc"
var wordDocument = WordprocessingDocument.Open(filePath, false);

What could be causing this error? Thanks!