I have acrobat 2020 and have lost my serial number, I purchased a new computer and wanted to transfer it from my old computer to the new computer. Can I extract the serial number from the registry somehow?

you have 3 ways to recover a serial number that you once had, but for you, see #2 below:

1. if you purchased from or registered with adobe (automatically done with cs6), you can check your account, https://accounts.adobe.com

 2. if your adobe program is installed on another computer you can recover its serial number from that computer,

(win:) http://www.belarc.com/free_download.html,

(mac:) https://mac-product-key-finder.com/

3. http://helpx.adobe.com/x-productkb/global/find-serial-number.html