Is there any easy/simple way to protect a .txt file with a password? So whenever open the file, password is required, just like opening .pdf with a password protected. Though I still want to be able to edit the text file in general text editors (notepad).
Use NotePad++ and add SecurePad Plugin. Check this link: http://www.addictivetips.com/windows-tips/encrypt-notepad-text-documents-with-securepad-plugin/
You can also use 7-zip, compress and encrypt the file together. Also for doc files you can use build in office functionality.