.NET Reflector 11.1 is a professional decompiler and debugging tool developed by Redgate Software. Regarding serial numbers and activation, here is the official information and procedures: Serial Numbers and Activation
Licensing: You can purchase a legitimate license directly from the Redgate website. Best Free & Open-Source Alternatives .net Reflector 11.1 Serial Number
Learning: It's an educational tool that allows developers to learn from existing code. Decompile
There are several reasons why you might need a .NET Reflector 11.1 serial number: Decompile .NET assemblies to C#