I have acrobat Pro Dc version on CD. Trying to install on my new laptop but it won't accept my serial number it says that it's not valid. I have the serial number on the receipt and on the box. Do serial numbers expire or do I need to re register my software?
It would not have to expire, perhaps because it was active on a machine before, you can enter your email account at Adobe.com or in the LWS to request support with this. Check the you followed links.
Acrobat DC does not require a serial number. It's a subscription based license that is tied to a specific Adobe account.
Are you sure you're installing the correct version?
I think I do because it's an older version 2015 and I purchased it in 2017.
That's possible. Confusingly, older versions of Acrobat without the subscription-model (so-called "perpetual license") were also called DC... Either way, you must use the correct installer for your serial number for it to work.