How to get the path parameter in voidMain function (Add program to Context Menu)

I will describe the step by step and my problems encountered when registering my program in ContextMenu.

In my solution, class MainTool used to process data in Excel File: read the content, logic, catch errors, exceptions, ... And when loading Excel file contents into the program must go through this class, so void main() function of I as follows:

static void Main(string[] args)
{

Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);

frmMain main = new frmMain();
MainTool.frmmain = main;

Application.Run(main);

}

And now, I am trying to register my program on ContextMenu (more comfortable for the user to choose a program to manipulate the right click directly on the Excel file instead of selecting from the program file Excel). I did the following:

public static void RemoveContextMenuItem(string extension, string menuName)
        {
            RegistryKey registryKey = Registry.ClassesRoot.OpenSubKey(extension);

            if (registryKey != null)
            {
                string extstring = registryKey.GetValue("").ToString(); //root

                registryKey.Close();

                if (!string.IsNullOrEmpty(extstring))
                {
                    registryKey = Registry.ClassesRoot.OpenSubKey(extstring, true);
                    if (registryKey != null)
                    {
                        RegistryKey subky = registryKey.OpenSubKey("shell\\" + menuName);
                        if (subky != null)
                        {
                            subky.Close();
                            registryKey.DeleteSubKeyTree("shell\\" + menuName);
                            registryKey.Close();
                        }
                    }
                }
            }
        }

and Instance method of frmMain:

public frmMain()
        {
            InitializeComponent();
        }

        public frmMain(string filePath)
        {
            InitializeComponent();
        }

Last job is to take the path of the Excel file and pass in the Main function:

[STAThread]
        static void Main(string[] args)
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            if (args != null && args.Length > 0)
            {
                Application.Run(new frmMain(args[0]));
            }
            else Application.Run(new frmMain());
        }

Registration program has been in ContextMenu, when selected to run the program but can not read excel file as well as data processing on it. I understand that, class MainTool not yet been assigned to frmMain. And I do not know how to solve this problem.

Or better way to register the program on ContextMenu when packaged applications that can meet the above purposes.

Thanks you very much!