Compare Two DLL's

I would recommend to disassemble two libraries with the Reflector (right click on the assembly -> Export) and then compare directories generated with some merging tool, like WinMerge.

This is a free option to compare .Net C # assembly: Assembly Diff Tool for .NET - JustAssembly

Today the same can be done with JetBrains dotPeek. Load the dll right mouse button -> export to project and compare in WinMerge