how to debug referenced library

Question

In my C# project(VS2012), I have a Main project that references a dll.

This dll is built on another project of C#.

I want to step into functions of dll project.

I am not able to debug into function of reference dll.

I have compiled dll & .pdb file in one of the folders of the Main project.

 

I am looking for a help how to resolve the above issue so that I can debug the dll function, without adding dll project to my main project solution.