You can just copy and paste the files themselves.
When you have your solution open, look at the top of the solution explorer and you’ll see an icon that looks like a page with a page outline behind it and a yellow page (not a very intuitive icon). This is the “show all files” button. Click that and you’ll see all the files in your currently selected project (it is project-specific). Highlight any files that you want to include, right-click, and select “Include in Project.”
