I have serial key not subscription -cant install

Hi I have a serial key for acrobat pro DC

I suspect you may have a serial number for Acrobat 2020, the perpetually licensed version. DC is the subscription product.

https://helpx.adobe.com/acrobat/using/whats-new-acrobat-2020.html

You should be able to sign in to your Adobe account and find a download link to Acrobat 2020 in the Plans & Products section.

Your serial number must match the version that you download... what did you download, and from where?

For serial number programs you may download ONLY if you bought direct from Adobe via download
-Log-in to your Adobe account and click this link https://account.adobe.com/products
--click Order history on the left and then the link to your order that will show on the right
--and finally click the link "Downloads and serial numbers" that will appear
---as always, write the serial number in a text file AND copy that text file and the
---download file(s) to an external drive (or two) to be sure you always have what you need
-if you did not buy direct from Adobe via download you must find your original install
-if you have an Education or volume license you MUST use your original media
--the link for an Education or volume license download is not available at all
-if you bought a disc and don't have a drive you will need to buy an external USB drive
-if you bought and lost a disc Adobe does not provide a replacement via download
-if you bought a download from a 3rd party vendor you will need to contact that vendor