If you have previously been granted a permanent residence permit, you can continue to live in Norway and do not need to apply for a new permit. NOTE: must not be confused with permanent right of residence (varig oppholdsrett).
You likely have a permanent residence permit if:
If you have a permanent residence permit and your residence card is about to expire or has expired, you must order a new residence card (external website).
You must also order a new residence card if you have a temporary residence permit that is still valid and you have lost your card, if the information on the card is incorrect, or if you otherwise need a new card.
If you have a temporary residence permit that is expiring and you do not meet the requirements for permanent residence, you can apply for a new temporary residence permit. See the information under "Application for residence after the application period has expired," but ignore the requirement to explain why the application was submitted late.