A 2017 key will not work on Acrobat DC or 2020 versions.
. Once added, the software should automatically recognize the license when you sign in to the application with that same Adobe ID. Finding Your License Key adobe acrobat pro 2017 enter license key
Since is a "Perpetual" (Classic) product, the screens look different than the modern subscription-based "Document Cloud" versions. A 2017 key will not work on Acrobat DC or 2020 versions
Here are some additional points to keep in mind: adobe acrobat pro 2017 enter license key