When you save your Word documents make sure you default save setting is for .docx files rather than .html files. You will have a drop down selection next to Save as type where you can choose what type of file you want to save your document as.
You can also check your Word save options to make sure that they are set correctly to .docx rather than .html. Click on File, Options and then click the Save tab. Where it says "Save files in this format" make sure its set to Word Document (*.docx). If it already is then I would try a repair installation or completely removing, running Ccleaner and then rebooting. Then reinstall after that.