You open PandaBank, click on the 'Help' tab and click on 'debug window'. There, you click on the 'Console' tab and you have to type in a command and enter your private key in it. I do not know the command because I don't intend on depositing my PND from paper wallets anytime soon. I think it is the 'importprivkey <pandacoinprivkey> [label]' command, though. Without the 's of course.

***This is not official and the developers had nothing to do with the creation of this***

I made a guide for keeping your PND safe to an insane level if you don't mind less interest. Nobody will know that the wallet exists other than the public address on the blockchain and it will be preserved if you use this guide correctly.