Lay 4 cut sheets of parchment out on flat, clean, dry surface and place a piece of salmon in the center of each sheet, skin side down. Season with salt and pepper. Divide juniper berry marinade among salmon pieces, drizzling it overtop each piece. Rub marinade in with your hands, lifting salmon and rubbing a bit onto the skin side before replacing it on parchment, skin side down. Fold parchment over salmon, crimping edges to seal. Lay parchment parcels on baking sheet and cook in preheated oven for 20 minutes.