You cannot use an native class/struct into managed code. You will have to create an equivalent class in your managed code. You can use visual studio to create an CLR application, using which you can create a reference class
which will work as a wrapper to your native code.
You will need to write a wrapper for each function you want to use. Writing a function is similar to writing functions for any other native class, and then you can reference the dll
in your windows service and use the functions like any other managed function.
You can refer to Quick-C-CLI-Learn-C-CLI-in-less-than-minutes for a quick example.