If you want to be completely secure, you should import your private key into an air-gapped device. Being offline at the time of importing the private key isn't enough.
And it may worth mentioning that, you will need two devices for making transaction from your paper wallet. One should be offline and one should be online.

You should create a watch-only wallet and create an unsigned transaction on the online device and sign the transaction on the offline device. After that you will need the online device again for broadcasting the transaction.