You do that from the console window by using the dumpprivkey command.
Take a look at this guide for reference:
https://en.bitcoin.it/wiki/Transferring_coins_from_Bitcoin-Qt_to_Electrum
I don't know the address or anything, I just have the .dat file itself from a backup (all the other info was lost) and the passphrase.
I'm willing to download the full blockchain again, that's not the issue, but I was wondering why there's no good info out there to really restore an old wallet file.
So if I have 2011.dat for example, and rename it to wallet.dat and place it in the bitcoin folder where the new wallet is then restart bt core then it should work?
I heard older wallet files were incompatible since 2012 or something.
PS: before anyone asks, no, there's not a fortune on there probably, I just want to make sure the balances were emptied, as I can't remember what I did with it back during these days. I didn't take bitcoin too seriously in the beginning (my bad).