A car dealer is required to guarantee there is no money owing on the car. They must also disclose all relevant information about the car, such as whether it has had flood or hail damage, if there has been odometer interference, or if there has been major modifications that may impact your decision to purchase the car. In some situations a dealer is obliged to provide a dealer guarantee to repair any defects the vehicle might have after you buy (this is formerly known as a statutory warranty).
Yes a contract of sale, and I would also say the vehicle safety inspection certificate as it is required to hold this at the time of sale. Since a dealer is required to guarantee that there is clear title to the car you shouldn't need to worry about the PPSR.