If the 12 words are given to you, that means the person or company that gives you the seed phrase will have it and have access to your bitcoin and steal it. Wallet will generate you seed phrase in a way only you will know the seed words. That is why it is good to use open source wallets like Electrum because close source can be malacious in a way malware can be included in a way the wallet will generate already known seed phrase or seed phrase that can be know to the developers of the wallet.