Articles

You should set KeyPreview property of the Form to True and use VertScrollBar property of your form to change position of the form.

procedure TForm1.FormKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if Key=VK_NEXT then
    VertScrollBar.Position:=
      VertScrollBar.Position+
      StrToInt(Edit1.Text)
  else
    VertScrollBar.Position:=
      VertScrollBar.Position-
      StrToInt(Edit1.Text);
end;