A private key is what control the funds, and make them spendable on its correlating public key.
We do not reuse a key pair (public and private key) after the private key has been swiped/imported on a networked computer, ie do not reuse a paper wallet after the private key has been used.
== Links, Guides and other helpful tips ==
https://en.bitcoin.it/wiki/Securing_your_wallet
https://bitcoin.org/en/secure-your-wallet
http://bitcoinsecurity101.com/getting-started/
https://virtopia.ca/crypto-wallet-safety/