Try using SoftMaker FreeOffice instead of LibreOffice.
You get it at freeoffice.com, it's a full-fledged, free office suite.
FreeOffice has very good import and export filters for Microsoft Office formats, and you should be able to open your docx without formatting losses. No other free office suite gives such excellent interoperability with MS Office in both directions.
Please note that opening docx works perfect, but saving is only possible as doc; if you need to save in docx, you require the pay-for version SoftMaker Office (which has also more features and templates, free technical support and an included macro language).
More info at http://www.freeoffice.com/