If the main document part of a DOCX document is with name different than "document.xml", for example "document2.xml", the content of the document is not imported. 

Such documents are created by OpenXML SDK, if for example this tutorial is followed:
How to: Convert a word processing document from the DOCM to the DOCX file format - http://tpdogfood.telerik.com/msdn.microsoft.com/en-us/library/office/gg188063(v=office.15).aspx.