Starting today, domestic train tickets are no longer sold on paper version. Passengers must use an OV-Chipkaart (and RFID-based smartcard)
Single-ride tickets will still be sold, loaded on a disposable card. However, they will come with a € 1 surcharge over the full fare price.
The OV-Chipkaart needs to be validated (by touching) at totems or electronic gates on the departure and arrival stations. Several stations that are fit with gates have now 'restricted areas' where only passengers who validated their cards can access (so you can't just go to the platform if you don't have a valid ticket). On these stations, the exit gates are opened when you tap your card at them, naturally.
Some gates are fit with technology to recognize QR codes printed on online tickets and those issued for international travel. However, this part of the system is still not worked out, so there will be station agents near gate barriers, where applicable, to manually open gates for passengers travelling on international paper tickets without QR codes.
NS (the national railway company) spent a lot of money and 9 years to make 'paperless travel' a reality.