No, that is the lest secure and most shared file and you cant password protect it.
The best thing to do is make an 256 encrypted Disk Image and store your sensitive data in there.
Mount it when you need access and eject it when you're finished with it.
That way you can store the info in any format you want, even TextEdit docs, and its totally secure.
Not even Apple can get to the data if you forget the password, be warned...