I have used inbuilt utility known as Open & Repair. Check out the steps here €“
https://support.microsoft.com/en-in/kb/893672
It helped me to fix my Word problems. More Tips for recovering word document file (.docx and .doc) -
http://msword.filerepairtool.net/blo...-docx-document
However it is not a foolproof solution. If in case it fails then it is highly recommended that you must third party Word Repair Tool software.