Look at the C# example in the SDK or here :
http://support.voidtools.com/everything/SDK/CSharp
You cannot import the DLL as a reference because it is not a .net wrapped DLL.
You need to add the dll to the project (as a standard file) and select "Copy to output directory" option in the dll properties.
Then, you can use the DLLImport statement (as seen on the above link) to be able to use the functions in your custom application.
Make sure to use X86 as target platform or you will get badformatexception errors.
Also, the example didnt returned any results for me until I used "run as administrator" to launch it (even as administrator and UAC disabled).
Tested in Vs 2013 RC on WIndows 8.1 x64
