I am using Ms Office 2007.This trick will only work in Ms office 2007 But You still can Put password with older version like 2003.I Think the way should be Same as this….???1. Open the document which you want to protect.
2. Now click on save as.
3. And then find tool named button on the save as dialog box or try the L key
4. And then on general option (if you can’t find the tool then try the L key and then g )
5. A dialog box general option will open
6. now type the pass word in password to open and leave the password to modify blank
7. click on protect document or press enter then reenter the password
8. now click on save Now when you try to open your document it will ask for password.
(Note :- THIS PASSWORD CAN BE EASILY BE BROKEN BY SOME PAID SOFTWARE,BUT STILL YOU CAN PROTECT IT WITHOUT AND WORRIES BECAUSE IT’S PAID SOFTWARE AS FAR AS I KNOW)