From Word, you can export as RTF and convert this to MOBI using Calibre. You may get better results by exporting to HTML (choose simple or "filtered" HTML) and then convert this to MOBI using Calibre.
Another option is to use LibreOffice (the better version of OpenOffice) and Writer2ePub to create an ePub from your DOC or RTF which can again converted to MOBI using Calibre. See
Quickest, easiest, cheapest way to create an ebook?