Click on the Sign button, and enter
your Armory wallet password, and the signed transaction will then be saved back to that same file:
One of the lesser known features of Bitcoin is that the private keys, which form the basis for a Bitcoin address, do not need to be generated randomly; instead, one can generate a Bitcoin address, fully compatible with Blockchain.info's
wallet and
Armory, using nothing but standard easily available cryptographic tools and a
password of your choice.