As part of my ‘Both Koreas in One Go’ journey, I had to have my NK visa arranged via a tour agency based in Beijing, China. The visa is NOT stamped anywhere in your passport. Instead, you will be handed in this tourist visitor card… just for a few minutes. Yes, the tour agent needs your visa to efficiently and securely deal with North Koran authorities. As far as I remember, I was in possession of it briefly at the Dandong train station, shortly before departing for Pyongyang. Moreover, once I got checked in the hotel, I was ordered to part with my passport for the duration of my stay. All paperwork was taken care of on your behalf by a tour agency. The whole process was smooth and kept under surveillance by NK authorities. Basically, the worry is not whether or not you will be allowed to enter the North Korea territory but whether or not you will be allowed to leave.
Some official info:
As of April 2017 holders of normal passports of all countries require a visa to visit North Korea. All visitors traveling for tourism require an authorization from a North Korean travel agency. An exception exists for Chinese tourists visiting only the Tongnim County who can stay in this county using the Chinese ID card instead of a visa and passport for up to two days. Most nationals may also visit Sinuiju for a day trip without a visa.