A ".dat" file can optionally be encrypted, which by all means should be.
There is a few different codes, keys, phrases and passwords and they are all critical in keeping your crypto safe!
A 12–24 word seed such as used on most HD and hardware wallets, which is deterministic of millions of addresses and potentially unlimited coin types, which can be demonstrated by using Mnemonic Code Converterhttps://iancoleman.io/bip39/.These seed words are rarely remembered by someone, rather should be stored safely.
Core wallet passwords are used to encrypt .dat files. Advanced users often choose to use a core wallet for better coin control (i.e. storing coin on single or separate blocks) Using the option to encrypt dat files will then require entering the chosen password before being able to do sensitive functions within the interface, such as send transactions. This password is is usually remembered by the owner/creator of the wallet
HD Wallet pin codes (such as Jaxx or Coinomy) utilizing a 12–24 word seed also has additional security once you have created or restored control of your assets from your device. Often these are 4–6 numbers, if they are forgotten, you can still restore using the 12–24 word seed. The pin code is often remembered by the creator
Private Keys which allow you to write to the blockchain which houses a particular address. If you are storing your Bitcoin (as example) on one particular address and have not moved it, a single Crypto key could gain access to it. If part of it has been spent, then the . remaining will move to a change address and no longer be on that address. This is the reason people prefer using simple wallets, which control the keys for them. Crypto keys are impossible to brute-force and are not remembered by the owner.