Here is a brochure in English:

https://app.artcloud.fi/vhvsy/vantaanjoki-2-en/?version=21172/

As stated, Ruutinkoski is another rapid close to Pitkäkoski. You can fish at Pitkäkoski and Ruutinkoski with Helsinki city fishing license or Vantaa city fishing license. Pitkäkoski and Ruutinkoski can be a bit challenging at times. No rainbow trout is stocked there, even though you might catch some that have flown down from Vantaankoski (which requires a separate, more expensive license). Nevertheless, it's a nice experience.

If you live in Helsinki or Espoo, you can by a combined license for Helsinki and Espoo at 17€ and this give you the permission to fish at these rapids, plus (for example) use 3 rods for white fish (siika) bottom fishing (pohjaonki) at Helsinki and Espoo fishing areas (please find the maps for these, this is not all shores in Helsinki or especially Espoo but still a very wide area). At the rapids, however, you can only use one rod, and should not be bottom fishing (pohjaonki) anyway, as live bait is not allowed - if you catch for example salmonoid that needs to released there is a higher chance the fish has taken the hook too deep to survive.