adding virtual printer using c#

Since you are looking for creating a printer's driver, you can check Windows Driver Development toolkit. It provides tools that can help you to develop, build, package and deploy your driver models. You can find more details here:
https://msdn.microsoft.com/en-us/library/windows/hardware/ff557573(v=vs.85).aspx
https://github.com/Microsoft/Windows-driver-samples
But keep in mind that you will need to wrap many Windows APIs to accomplish this in .NET.

Alternatively, you could try high-level virtual printers features from LEADTOOLS that provides ready .NET classes to create your own virtual printer, which should behave similar to any printer’s driver.
You can find more details here:
https://www.leadtools.com/help/leadtools/v19/dh/pr/printer-printer-install.html
https://www.leadtools.com/help/leadtools/v19m/dh/to/pr-topics-programmingwithvirtualprinterdriver.html