It is NOT, and should not be held down with adhesive of any kind. The part is fixed by soldering only. The thin metal tab must be soldered down to the strip on the PCB, not only for electrical connection, it also serves to dump excess heat from the device to the copper layer on the board.
Use a large soldering iron to do this, first level off or remove the solder on the horizontal strip so the new device can lie down flat, then solder the pins to the board to hold it in place, finally solder along the tab to the horizontal strip. By design the tab and board are there to move heat away, hence needing a big soldering iron but try to do it as quickly as possible to avoid damaging the new part.
Brian.