On the rare instances that I've had to password protect a folder (at work) I've used an encrypted disk image to store, save and work on confidential files. You don't need a third party app for that, so it's possibly worth experimenting with at first to see if it's a workable solution for you.
Thanks for your reply.
I am looking for some 3rd party application because it can make the job easier, can have more option and protect any single file or folder. Does anybody has experience using espionage? Can it do the job as it said.
Thanks