2. you can check your account (if you purchased from or registered with adobe AND you remember the adobe id used to purchase/register), https://accounts.adobe.com
3. if your adobe program is installed on another computer you can recover its serial number from that computer,
p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post if it helps you get responses.
If you registered the software with Adobe, you can login to your account here and view the old serial numbers. If you did not register and you bought from a third party you can try to go to them for the serial.
However, with that said, your license does not guarantee that it will run on a newer computer. Acrobat DC may no longer work with Windows 11 or Mac OS 13 so all this may be for nothing.