PW,
I'm surprised that your tour instructions are not very specific.
As far as I know, there is no direct bus from the airport to Padova, but I may be incorrect. Perhaps it's best for you to contact the RS office for more information.
The following information is for the bus from airport to Venice Mestre train station, then train to Padova:
Since you will be traveling to Padua (Padova) via train, you can take the 'ATVO Fly Bus', which runs between the airport and the Mestre railroad station.
Here is a very informative website with details as to where to find the bus:http://europeforvisitors.com/venice/mestre/mestre-airport-buses.htm
You can check bus schedules here: http://www.atvo.it/index.php?lang=en&area=23&menuid=35
You will want to click on the icon (blue circle with white arrow) next to: 'Aeroporto Marco Polo di Venezia - Mestre F.S. (servizio espresso)' -- 2nd one from top.
The schedule is valid through August 31, but will be updated shortly.
You can check train schedules here:http://www.trenitalia.com
You will need to choose the train stations (Italian names) from the drop down menu as follows:
- From: Venezia Mestre
- To: Padova
Both the buses & trains run late and frequently.
Hope this helps!