unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls, ComCtrls;

type
TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    Edit2: TEdit;
    procedure Button1Click(Sender: TObject);

private
    { Private declarations }
public
    procedure MyCopyDataMsg(Var Msg : TMessage); Message WM_COPYDATA;
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
cdds : TCopyDataStruct;
begin
cdds.dwData := 0;
cdds.cbData := length(Edit1.Text)+1;
cdds.lpData := pchar(Edit1.Text);
SendMessage(Handle,WM_COPYDATA,0,LongWord(@cdds));
end;

procedure TForm1.MyCopyDataMsg(var Msg: TMessage);
var
cdds : TcopyDataStruct;
begin
  if msg.Msg = WM_COPYDATA then
  begin
    cdds := PcopyDataStruct(Msg.LParam)^;
    edit2.Text := (Pchar(cdds.lpData));
end;
end;

end.