// declare, configure and open port
System.IO.Ports.SerialPort com = new System.IO.Ports.SerialPort();
com.PortName = "COM1";
com.BaudRate = 115200;
com.NewLine = "\n";
com.Open();

//read whole file content to string array
string[] lines = System.IO.File.ReadAllLines("c:\myfile.nc");

//iterate each element of array
foreach (string line in lines)
{
    //write on serial line
    System.Diagnostic:Debug.Write(line);
    com.Write(line);

    //wait for response
    string rv = com.ReadLine();
    System.Diagnostic:Debug.WriteLine(":" + rv);
}