I have a few dll files in \\lib folder of my project folder. In the property page of dll, I have selected \"Build Action\" as \"Content\" and \"Copy to Output Directory\" as
I had the same problem with Visual Studio 2010 / C# Project.
For assemblies (i. e. having the .NET interface) use folder "References" under your project in the Solution Explorer. Right click it, choose "Add existing item" and locate your .dll assembly.
Common .dll files can be placed in a subfolder (as "\lib" was mentioned above) and in the properties select:
This worked for me exactly as desired - during build, the .DLLs are copied to the output directory without the "\lib" subfolder.