In Word, click on Tools | Customize | Keyboard | Categories: File
| Commands: FileNew | Current keys: Ctrl+N | Delete | Close. If
you are prompted to save changes to your Normal.dot global
template when you exit Word, say yes.

Chris at FCC wrote:

I want to remove the Ctrl + N shortcut key from Word (I keep hitting it
accidentally, and never use it to open a "New Blank Document" anyway). I
tried following the instructions in Help, but the key does not show up on the
current shortcut list in Tools-Customize. I even tried adding it and then
removing it, and I still get a new document when I hit Ctrl + N.