I have bought a few after effect project files and they are not as long as I need so I want to take complete scene from one and duplicate it and add it on to make it longer. I know how to duplicate a layer and how to extend a timeline so that is not what I am asking.
If anyone can help this would be great!
this is a bit complicated and depends how the project had been build.
in simple terms in most of the projects you need to duplicate a number of nested compositions.
this plugin can help you with this processhttp://aescripts.com/true-comp-duplicator/
but the time consuming part is to understand how each template is build and how the components are working together.