Many online searches for "Adobe Illustrator CS5.1 amtlib.dll" lead to "cracked" versions of the file. It is highly recommended to These files are frequently used as "Trojan Horses" to deliver malware, keyloggers, or ransomware to your system. Always use the original installation media or digital installers provided by Adobe. Conclusion
: Bypassing activation software is a violation of copyright law and Adobe's licensing agreements. 🔧 Resolving "Missing" or "Corrupt" Errors amtlib.dll error - Adobe Community
If you simply need to open old .ai files from CS5.1, consider using the free or Photopea (online) instead of cracking the software.
If you are a legitimate owner, use the official Adobe Cleaner Tool or restore from a trusted backup. Avoid third-party DLL download sites at all costs.