Train from

Looks like you need a train from Fiumicino Airport to Padova. That usually involves taking the Leonardo Express train from the airport to Roma Termini, then a direct highspeed train to Padova. Since I assume you want to go to Padova straight way after landing, just wait and buy the ticket after you get through passport control and have your luggage. You cannot predict if the plane will land on time and how long to get through passport control. Should be a direct train from Termini to Padova at least every hour.

Anyway, it is way to early to book a train 11 months from now. Currently there is a direct Frecciarosso highspeed train from Termini at 35 past the hour every hour and it takes 3 1/2 hours to get to Padova.

Consider spending a few nights in Rome before heading to Padova

Or fly to Venice and spend few nights there-Padova is just a short train ride from Venice