[Nora]

Код:

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

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    Edit2: TEdit;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
   StrNew:String[255];
implementation
function MyFunc(str:string):string; stdcall;
external 'PrDll.dll' name 'ChangeString'; 
{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);

begin
   StrNew:=Edit1.Text;
   MyFunc(strNew);
   Edit2.Text:=StrNew;
end;

end.