Just to add to ensure it is clear that you cannot apply to renew a PR card from outside Canada. If you have been outside of Canada for 4 years and plan to come back at any time you will need to apply for a PRTD which will highlight the failure to meet the residency obligation possibly leading to your pr status being revoked. The only exception to the latter could be if accompanying a citizen abroad for which you would need to show documented proof or if holding a US passport you could take your chances of not needing to show a PR card or PRTD to fly back..