Is your DLL a COM DLL? Then you need to #import the type library into your app. Is your VS project a .Net app? That's what adding the reference in VS is doing for you behind the scenes.

You still cannot link to it statically. It's a DLL. Your VS app is loading it at runtime even if you don't think so. Build your app, then move the DLL somewhere (or rename it temporarily), then run your app without rebuilding. It will tell you it can't find the DLL.