The Adobe Creative Cloud Desktop App is free to download and install. It acts as a launcher and manager for Adobe software. However, using the creative applications (Photoshop, Premiere Pro, Illustrator) requires a paid subscription or a free trial.
Adobe maintains a hidden directory for enterprise users. Go to:
https://creativecloud.adobe.com/apps/download/creative-cloud-desktop-app
A: You have downloaded an ancient version (pre-2013 Creative Suite). The modern Creative Cloud model does not use serial numbers; it uses your Adobe ID login. Delete that installer and get the one from the links above.