You want to add an existing file to your project, but you don’t want to create a copy.
When adding an existing item to your project, select the Add As Link option in the Add Existing Item dialog box.
When adding an existing file to a project, the file is copied into the project folder. The Add As Link option allows files to be shared among projects, which eliminates duplication. As a result, you can share files that contain reusable classes, methods, constants, and even settings across your applications.