When you complete your returns with a TurboTax CD/Download product, your returns are stored locally on your hard drive. This means if your friend is using a separate computer they won't be able to access your returns.
Yes you will have to supply the License Code.
Please see the below for additional information:
You’ll only need to enter it and validate the first time you install on a computer. You can, however, install the software on up to five of your computers using the same license code. If you need more, you’ll need to purchase another TurboTax license.
What if tho people share the same License/Activation code (say family member filing separately or friends).
I understand it may not be recommended but still to be clear:
Is there a way for person 1 to know about the person2 who usd the same code?
You’re free to use the same license code to install the software on up to five computers, but you'll need to purchase another license if you need more. For more information on how to use the activation code, please see our Help Article.
[edited 4/14/23 3:40 PM CDT]
No. Your tax return is saved in a separate data file ending in .tax2021, .tax2022 etc. It is only saved and stored on your computer. If Turbo Tax program is installed on another computer it doesn't have access to any other returns done on another computer or done in the Online version.