I have fou.dll that also needs friendfou.dll When I compile my project friendfoul.dll is being pulled into my bin folder from somewhere, I can tell because I delete friendfoul.dll and it reappears on compile.
How can I tell where friendfoul.dll is being pulled from?
Open the Solution Explorer, expand the project's References node and open the Properties window of the fou.dll reference. You will see the path from where it is being copied.
If you open the project file (*project_name*.csproj for a C# project, for instance) and look for the entry with the entries, you can find the info you seek there, I believe.
Since you said in comments that friendfou.dll is not a reference of your project, try looking at a build events if dll is copied from somewhere. To find build events, go to project properties, on build events tab and look at pre-build or post-build event command lines and see if there are any references to friendfou.dll