Betty,
1. Simply do a "Save-As".
2. Select the "Tools" menu, found on the right side of the save-as dialog box.
3. Select "Security Options".
4. Enter a password in the "Password to Open" field, if you wish to keep
people from opening it altogether.
5. Enter a password in the "Password to Modify" field, if you wish to allow
people to open the file, but requires your password to alter it.
If you do both, then they can neither open it nor alter it without the
passwords. Be carefule with this though, as you want to make sure you use a
password you will remember, yet others will not know. You don't want to lock
yourself out of your own document.