How to create new project with existing files with C# 2014

I have been asked to modify an existing C# program (with a wpf file included) and then create an executable (published) file

The problem is that the existing project is absolutely knackered, I only want to include all the necessary files and disregard all the crap

I created a new project and then added all existing files, the trouble is all the forms show a blank form and so I must have to some how tell the project to marry the form designer file with the form file

Is there any tutorials on how to do this

Thanks