Re: Just set Windows to open in the ms Word Viewer
OpenOffice/LibreOffice might not render documents faithfully, but then MS Word does not have a good track-record in that respect either (between versions). I'm not sure either whether Word will cope with printer drivers and fonts on the source machine differing with those loaded onto a target machine, which would cause rendering to be affected..
There shouldn't really be a need, other than collaboration on document assembly, for documents to be sent in docx format anyway. That's what pdf is for. Having said that, Adobe have shot themselves in the foot for enabling the possibility for malware to be embedded in that format.