Armory wallet does not work if your Bitcoin core is pruned it needs to download the whole blockchain to make Armory work and the current blockchain size is not 435GB it's more than 500 GB.

About extracting the private key you can backup the private key by going to wallet properties> backup> export key list.

If you don't want too much hassle then use Electrum wallet you can import private keys from Armory to Electrum wallet.