Dear @Theodoros Andreou
The 2017 will be either the 3.5 or the 3.8. The 3.8 model will have the 3.8 label on the backside and also when you open the bonnet you will find the large MIVEC logo on the engine cover. If that is not there i would say it's probably a 3.5.
The car has a timing belt, if there is no service book i would highly recommend to get the belt done. Better to spend on a belt than to replace the engine. I think 120k is the belt service but not 100% sure.
The car has a brain (ECU) but will not show last services.
My opinion: if there is no service history or book from the previous owner: WALK AWAY. There are tons of nice Pajeros for sale with full service history from the dealer, so i believe it's not worth the risk, unless the price is REALLY very low.