Adobe offers various plans, including individual and business plans. For most users, the "All Apps" plan, which includes Illustrator, Photoshop, InDesign, and more, is the most cost-effective way to access the software.
: If you purchase Adobe Illustrator directly from Adobe or an authorized reseller, you should receive a serial number via email or it's embedded in your purchase confirmation. adobe illustrator 90 serial number link
To download Adobe Illustrator 9.0, look for legitimate sources: Adobe offers various plans