I guess that what @mocacinno has shown is probably perfect.
However, as a super-simple method with similar results, isn't 7zip with AES 256 encryption good enough? Imho it's much easier to use...
7zip is easy to use and it does use that encryption type. If op is not satisfied with the result then why not use multiple encryption app like winrar too. To make it more secured, encrypt the file using 7zip with password enabled then encrypt it using winrar and add password too then back to 7zip to encrypt it again with password.