Files that have been protected using EFS are encrypted at the file-system level. The benefit of this is that the files can only be opened by the user with the appropriate private key and certificate. Even if you were to reinstall the operating system, the files would still be inaccessible.

You can encrypt a file using the steps listed below. An important point to remember is that a file can not be both encrypted and compressed. If compression is enabled, it will be disable when encryption is enabled.

1. Double click the Computer icon on your desktop and locate the file you want to encrypt.
2. Right click the file and select Properties
3. From the General tab, click the Advanced button.
4. Select the Encrypt contents to secure data option.
5. Click OK.
6. Click OK to close the file’s properties dialog box.

Once you complete these steps, the contents of the file are encrypted. When you access the file, the contents are automatically decrypted. You can disable encryption on a file by completing the steps outlined above and removing the check beside the Encrypt contents to secure data option.