The answers here are good for the time the question has been asked. In the meanwhile, IMHO, dnSpy has outperformed them.
✓ Visualize as C# or VB.NET - or IL
✓ Navigation between classes - by Ctrl+Click
✓ Examination of resources - live preview
? Handling .NET since 2.0 - I could not find such an old program for testing :-)
✓ Exporting classes to source ...
Syncfusion Essential PDF can be used to create and manipulate PDF using C#.
Live samples for ASP.NET Core, but the libraries are supported on Windows Forms, WPF, Silverlight, ASP.NET and ASP.NET MVC, WinRT, Windows Phone, Windows store universal and Xamarin applications as well.
A single license for the File Formats Edition costs $995. The whole product is ...