Using C++ a DLL has a structure similar to an executable file, which can be subdivided into a few main sections.
When the library is loaded, it is executed immediately the code relative to the Entry Point: the DllMain function (the EXE file has as its entry point the function "Main").
But the rest of the file consists of exported elements, commonly functions, that the programmer can import directly and independently from the main program.
I just checked my EagleGet folder and the id.dll file was not there. I updated to latest version of EagleGet, and the file was still not there. Maybe it was only included with old versions.