Word version 15.36 not working on MAC version 10.12.6

Hi!

I need help. Every time I start my computer an open a word document I have been working on, it doesn't let me save the changes. 

For example, I change something in my document and then, when I attached that document to my email, the changes aren't saved, so I lose all the changes and new information I put in. 

Please help me! I am doing my dissertation project and have lost a lot of information because if this problem. 

Thank you very much!