Permit from Timor Leste authorities as far as I know.
You would need to find which airlines fly into TL and contact them as to whether they take pets.
The problem you may have is that there are no direct flights from Portugal to Dili and so you would have to have 3 different flights with stopovers or transfers.
You could look at flying into Bali Indonesia and then to Dili or fly into Darwin Australia and then across to Dili.