If I do the following google search "developer.apple.com keychain", it gives me a web browsable version with a pdf link in the upper right. If I click the PDF link, I get the content for "every page" which means, in this case, the "keychain services programming guide".
In visual studio go to Help -> "Add and remove help content" and that will allow you to download entire topics like .net 4.5 docs.
You can even throw whatever you download on a network, and anyone can access it from there rather than individually needing to download it. That requires setting something in the registry though to access from the network (let me know if you want to know though).
If I do the following google search "developer.apple.com keychain", it gives me a web browsable version with a pdf link in the upper right. If I click the PDF link, I get the content for "every page" which means, in this case, the "keychain services programming guide".
I have yet to be able to do the same under msdn.