Apple pastila is a dried fruit product, so the main storage concerns are moisture and air. After opening the 2 kg package, keep the pastila in a cool, dry place away from direct sunlight and strong heat. If the original packaging can be resealed, close it tightly after each use. If it cannot be resealed, transfer the pieces to an airtight container.
Moisture is the biggest issue: if the pastila absorbs humidity, it can become sticky, soft or even develop mould over time. On the other hand, if it is left exposed to dry air for a long time, it may become harder and less pleasant to chew. An airtight container helps keep the texture stable. A refrigerator is usually not needed for this type of dried fruit confectionery; a cool cupboard is enough unless the label says otherwise.
Because the package is large, you may want to divide it into smaller portions and keep only one portion out for everyday snacking. This reduces how often the main package is opened and helps the rest stay fresh longer. Always check the best-before date and the storage instructions on the label, and if the product develops an off smell, visible mould or an unusual texture, do not eat it.