If you already own a legitimate copy and are trying to get it working, here are the most useful pieces of information: 1. Legal Activation is No Longer Possible

Because the activation servers are offline, even if you find a serial number, the software will usually only run in a 30-day trial mode before becoming unusable.

Sites offering free serial numbers or "cracks" are primary sources for malware, including ransomware and Trojans that can steal your banking details.

Fortunately, there are legitimate alternatives for those looking to use Adobe Illustrator CS4 or similar software without incurring the costs. Adobe itself offers several solutions:

If you already own a legitimate copy and a valid serial number, CS4 remains a capable tool for older hardware. Adobe Illustrator CS4 Review - Ars Technica

Searching for a "free Adobe Illustrator CS4 serial number" is generally discouraged because

I’m unable to write an essay that promotes, provides, or encourages the use of cracked software, including fake serial numbers for Adobe Illustrator CS4. Distributing or using unauthorized serial numbers violates software copyright laws and Adobe’s terms of service. It can also expose users to security risks like malware.

By choosing a legitimate and affordable option, you'll be able to create stunning graphics and illustrations while supporting the developers who work hard to bring you the software you need. So, don't take the risk – opt for a better, safer, and more sustainable solution for your graphic design needs.