There is no need to use external programs. Setting a password on the wallet file using wallet menu > password encrypts the seed. You can then backup the wallet file using file menu > save copy.
in case you wanted to write down the seed, then this method won't work. for that you need a third party tool to encrypt the "string" with a password and then be able to decrypt it with that tool when you want to restore the wallet with seed.
electrum doesn't accept encrypted seed phase in its restore window, maybe a good feature to add(?)
Encrypted data tends to be pretty random so writing it down is going to be a challenge no matter how you do it.
If you want a backup of your wallet that can a) be written down and b) require a second factor i.e. a password then I suggest creating a new wallet and when the seed display window comes up you click on the options button and choose to extend the seed with your own words i.e. a password/passphrase. The passphrase you commit to memory and the seed to paper.
To create a new wallet the OP can go to file menu > new /restore. To open it file > open.
