You do not need to copy GleamTech.ExamplesCore related code from the examples. That namespace is only for our Example Explorer (Live Demo) so it's used for demonstration purpose and it's not part of the actual DocumentUltimate library.
Instead, you should refer to the documentation, for example see this "Getting Started" instructions for a ASP.NET MVC project:
http://docs.gleamtech.com/documentultimate/html/using-documentultimate-in-an-asp-net-mvc-project.htm
However if you really want to use controls like ExampleFileSelector from GleamTech.ExamplesCore namespace, you can install it via Nuget Package Manager:
Install-Package GleamTech.ExamplesCore