On the properties page for files or folders, click Advanced, and check "Encrypt Contents to Secure Data". This will prevent other users signed in from other accounts from having access. But anyone signed in to your account can see and use them.
FileBuddy is a free encrypter:
http://www.jcmatt.com/filebuddy.html
FileBuddy is a free encrypter:
http://www.jcmatt.com/filebuddy.html