You can do this as follows.
Paste the following string in the program RUN (Windows Key + R)
or create a shortcut with it.
This will open your profiles folder and there you will find a folder ending with .default.
If you open this folder you will find a file called mimeTypes.rdf.
First make a backup of this file !
Then click the file and choose Wordpad from the option that Windows gives you when asking what program to use to open the file.
(If you would choose notepad the data in the file will be harder to read).
Now find the entry you want to delete.
For example DOC :
And remove the entire entry.
Keep in mind that some apps have more than one entry.
If things don't work out as they should be,
you can copy your backup (mimeTypes.rdf) in the folder, and start over.
You can delete the file if you want, to delete the entire list.