Which version of Word? Versions before 2007 were not very secure but 2007 is pretty secure (some details on this website -
How safe is Word 2007 encryption?)
What kind of data is it? Does it need to be edited? Who are you trying to stop getting hold of it?
If it does need to be edited then having lots of layers is probably counter-productive - people won't bother because it's too difficult. Even if it's only going to be read then you run the risk that the user will just copy the data somewhere else.
If this is a list of "in emergency" details which you don't expect to ever be read then you can safely use lots of layers as long as you've got clear docs about how to unwrap the onion :-)
Finally, it may be overkill, but
Windows Server 2003 Rights Management Services might be worth a look. Using this, you can specify who's allowed to open a file and, having opened it, what they can do with it (so, for example, you can open the file and read its contents on screen but you can't forward it to someone else, can't copy/paste from it and so on)