// In the PageControl's OnMouseDown event handler:
procedure TForm1.PageControl1MouseDown(Sender: TObject;
 Button: TMouseButton; Shift: TShiftState; X, Y: Integer);
begin
 PageControl1.BeginDrag(False);
end;

// In the PageControl's OnDragDrop event handler:
procedure TForm1.PageControl1DragDrop(Sender, Source: TObject; X, Y: Integer);
const
 TCM_GETITEMRECT = $130A;
var
 i: Integer;
 r: TRect;
begin
 if not (Sender is TPageControl) then Exit;
 with PageControl1 do
 begin
  for i := 0 to PageCount - 1 do
  begin
  Perform(TCM_GETITEMRECT, i, lParam(@r));
  if PtInRect(r, Point(X, Y)) then
  begin
  if i <> ActivePage.PageIndex then
  ActivePage.PageIndex := i;
  Exit;
  end;
  end;
 end;
end;
// In the PageControl's OnDragOver event handler:
procedure TForm1.PageControl1DragOver(Sender, Source: TObject; X,
 Y: Integer; State: TDragState; var Accept: Boolean);
begin
 if Sender is TPageControl then
  Accept := True;
end;