How to password protect a file?

Hi, I want to protect my files with a password when I open a document. I hope someone can help. Thanks.

Best thing to do is create an encrypted disk image using Disk Utility. It is pretty simple to do, and if you opt to not save your password in the keychain, you’ll have to authenticate every time you double click on the disk. It will act just like the DMGs you download, except that you’ll be able to write to it. It mounts on the desktop like a drive, and once you unmount it, everything in it will be protected again. Also, this is better than simply putting a password on something, because you can usually get around passworded files just by not using the program to look at them. Encrypted files, on the other hand, are much more safe.