how to add image/file to assembly from computer storage using C# code

I want the following functionality in my code so, I can save files or images to assembly of my project from computer for latter use

`

SetHeaderImage(openFileDialog1.FileName);


private static void SetHeaderImage(string filePath)
        {
           WindowsFormsApplication.Properties.Resources.add(filePath);
        }

`

Actually I need this functionality to set the image for invoice header to which can I embed in my Project.exe file.