Put the file in a folder and put it in a zip file(zip file 1)and then put this zip file in another zip file (say zip file2).Now open the zip file2 and then inside you will find zip file 2.just hishlicht it and go to file > add a password. Now give your password and then your confirmation password and the file is highly safe from piracy.
Note : you cannot send a zip file inside another zip file using the "send to" context menu. Just create an empty zip file and then cut the zip file 1 and open zipfile 2 and paste it in there.
If you have shared users you might also want to encrypt files . See how to encrypt files.
Also see How to restrict other users and have a highly secure shared computer.