How can i show outside boundary of my PCB board in pdf export?

There is more than one way to skin a cat... well... not that kind of cat...

Place the Copper Fill Blocker on the board, framing the saw line border... then click Routing, Copper Fill, then Copper Fill().

You can remove the Copper Fill Blocker. If you are not using Copper Fill then just cut around the copper edge.

If you are using copper/ground fill, then right click on the copper fill border, then click Lock Part. Once again, click Routing, Copper Fill, then Copper Fill() or Ground Fill(). Then just cut around the the Copper Fill Keepout...