What do you want to do with it? If you are a skilled programmer, you can figureout what the original code does, and try to recreate the source. You can never get the source code back from binary. You loose the comments ,variable names etc. All you can get is a mess of statements. If security is enabled, you get nothing.if ever the chip is protected is there a way to decrypt the code?
Unfortunately that is exactly what you are asking to do by 'transferring' their code into a new MCU.I'm not looking to copy someone else's work thats sure,