I would use OpenSSL, but that's just me...
$ openssl enc -aes-256-cbc -salt -in naughty-doc.txt -out naughty-doc.encrypt
This will prompt you for a passphrase, now.. that can be a password, but it can also be a phrase.. you'll definitely need to remember the grammar & capitalization though.
If you decide to use a password, make it a long and complex one...
To decrypt the file:
$ openssl enc -d -aes-256-cbc -in naughty-doc.encrypt -out naughty-doc.txt
You can obtain a list of ciphers via:
$ openssl enc -h