Preheat the oven to 425°F and prepare 2 sheets of parchment paper packs. Lay them separately on a baking tray. In a small bowl, combine the broth, lemon juice, minced garlic, and chopped parsley.
Season both sides of the salmon with salt and pepper. Drizzle the broth mixture over the salmon fillets. Place together the pak choi inside the parchment paper packets.
Divide the butter cubes over the salmon fillets and pak choi. Wrap up the paper packets in and fold the edges together.
Transfer the salmon paper packs to the prepared baking tray and bake them in the preheated oven for about 10 minutes, until the salmon and pak choi are cooked.