I've installed Windows SDK and one tool that came with it is Microsoft Help. With Microsoft Help you can choose what documentation you use online and which to download as a local help. And part of the selectable documentation is Visual C# and .NET Framework 4.
The link above is for Windows SDK main page. Latest SDK supports Win7/Server2008R2 and .NET 4 but it covers also earlier versions from WinXP (SP3) and .NET 2.0 (SP2). Downloadable documentation covers not just Visual Studio products and .NET Framework but also Windows Phone, Office and SharePoint etc.
I highly recommend downloading the package (although it's very large). It comes with a few handy development tools also.