Can I do this???????? Very important!! HELP

I have a pages document that I need protected. Is there any way to encrypt it and some how make it so you need to enter a password to open and read it. I don't care if I have to put this in a special locked down folder but I can not figure out how to do that either. This is a very sensitive Doc that can only be accessed by me and my wife so I need to do something other than just hiding it deep in my documents. I do not want to lock down the whole mac because my kids use it sometimes. I just need to lock this pages doc or a folder containing it. Any help with this would be great. Thanks guys.

Open Disk Utility and make a new Disk Image in File => New => Blank Disk Image. You can then select to make it encrypted with a password.