dll을 사용 compile시 Error가 발생하네요.
Compile Path가 문제인가요?

unit Unit1;

interface

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

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

var
  Form1: TForm1;

implementation

{$R *.DFM}
function ed(ss:string):string;far;external'edit.dll';

procedure TForm1.Button1Click(Sender: TObject);
begin
  edit1.text:=ed(edit1.text);

end;

end.