have you tried tagging your method as:
[ComRegisterFunction]
public void read()
{
String sFilepath = @"C:\Users\admin\Desktop\TestService Projects\DATA\Read.txt";
System.IO.StreamWriter oStreamWriter = new System.IO.StreamWriter(sFilepath, true);
Connection con = new Connection();
string[] result= con.read(4, Connection.baudrate.B19200, Connection.Parity.E, Connection.Databit.EIGHT, Connection.Stopbit.ONE, Connection.RegisterType.HoldingRegister, "1", 10);
for(int i=0;i<result.Length;i++)
{
oStreamWriter.WriteLine(result[i]);
}
oStreamWriter.Close();
}