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protected
  procedure CreateParams(var Params: TCreateParams); override;

{...}

procedure TForm1.CreateParams(var Params: TCreateParams);
const
  CS_DROPSHADOW = $00020000;
begin
  inherited;
  Params.WindowClass.Style := Params.WindowClass.Style or CS_DROPSHADOW;
end;					

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  published
    procedure SetShadow;

procedure TForm1.SetShadow;
  if SHADOW then
  begin
    SetClassLong(Form1.Handle, GCL_STYLE, GetClassLong(Form1.Handle, GCL_STYLE) or CS_DROPSHADOW);
  end
  else
  begin
    SetClassLong(Form1.Handle, GCL_STYLE, GetClassLong(Form1.Handle, GCL_STYLE) xor CS_DROPSHADOW);
  end;
  FormEinstellungen.RecreateWnd;
end;