Macs come with a Trial copy of MS Office, which is very nice, but I have never.. Will never spend $300 on Office. So, I removed it. The MS doc format is my favorite for saving stuff, because everyone uses Word or the doc format. Surprisingly, when I removed Office it left the file association alone. When I tried tried to open a file in doc format saved with TextEdit, boom “Error!”.
It turns out that file associations are even easier to change than Windows, which is really saying something. Just right click a doc file and choose Get Info. Expand “Open With”. Choose something from the drop down and click the “Change All..” button. Done.