Sorry for asking silly question.
Suppose i have 1 BTC in my wallet and I take a backup of it. Then i send that 1BTC so some other address and my wallet becomes empty.
And now if i restore that backup which i had taken while it was having 1BTC. Will i get duplicate BTC which i already spent?
Its not possible.
The data about you have this much money in your wallet is in the blockchain and that blockchain is not completely under yours or anyone's control because its decentralised.
When you spent it will be there in the blockchain.
When you backup the wallet, you backed up your key to access your wallet address.
Technically, you can do it if you can do a 51% attack on bitcoin network, LOL!