Can I see inside a dll file for methods or classes that are in a DLL file?
You can add them to Visual Studio, as described in other answers, but if you want to see the code and don't have .pdb, then you can use ILSpy (replacement for .NET Reflector)
See ILSpy Download Page
Add a dll to your project, then to visual studio
View menu → Object Browser
.net dll .NET Reflector, ,