Bob has given lots of useful information about how ME allocates its resources and doesn't free them up until you reboot. You might like to do a search to bring up some useful explanatory sites which have been mentioned on this Forum about resources and how you can get more by removing unnecessary items from the start-up menu.
I find with both Word and Excel that if I open either one, then close again, then try to re-open, I often have insufficient resources (depending on what else I have opened in the same session). It is better for me at least either to open them and keep them open, or reboot before trying to re-open them.
If you are saying that you cannot open Word after a reboot, even with 67% resources available, you might have a different problem that I'm sorry I wouldn't know the answer to.
(FYI I've just opened Word with 38% resources, which promptly dropped to 27%, and Word was workable; I opened a couple of files.)