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
If your main intent is to include DLLs without cluttering up the project root directory, another solution is to move the DLLs to a separate Shared Project and add this as a reference in the original project.
(Note that this post doesn't directly answer this question as it doesn't preserve the folder and project structure, but I found this approach useful because I was able to restructure my project in my case and because I wanted to avoid some of the downsides of the other approaches here.)
Steps
Solution -> Add -> New Project -> Shared ProjectBuild Action: Content and Copy to Output Directory: Copy Always)References -> Add Reference -> Shared ProjectsThe setup looks like this: