Quickly select assemblies to decompile and debug using the .NET Reflector add in menu in Visual Studio. Decompiled assemblies are saved for future use. Now you can step through debugging of any decompiled assemblies as if they were your own.
Set breakpoints, watch variables, set next statements, modify variable values, or use any of your other regular debugging techniques.

Developers use .NET Reflector VSPro to:

Debug assemblies without source code using the Visual Studio debugger
Decompile and explore .NET assemblies inside Visual Studio
Serve as a powerful object browser
Decompile .NET code to understand how it works
Learn or teach the complexities of a .NET language
Provide a better alternative to library documentation
Recover lost or unavailable source code
Locate performance issues
Analyze dependencies
Check obfuscation