[voron_paa]

Или включить функцию в тело класса формы...

Код:

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    OpenDialog1: TOpenDialog;
    procedure Button1Click(Sender: TObject);
    function open1:string;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
function TForm1.open1:string;
 begin
  if OpenDialog1.Execute then
   result := OpenDialog1.filename;
 end;
procedure TForm1.Button1Click(Sender: TObject);
var
name:string;
begin
name:=open1;
end;

end.

У тебя же объект находится на форме...

или... как вариант..

Код:

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    OpenDialog1: TOpenDialog;
    procedure Button1Click(Sender: TObject);
    function open1:string;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
function open1(OpenDl : TOpenDialog):string;
 begin
  if OpenDl.Execute then
    result := OpenDl.filename;
 end;
procedure TForm1.Button1Click(Sender: TObject);
var
name:string;
begin
name:=open1(OpenDialog1);
end;

end.