When you are travelling, you need a permanent resident (PR) card to prove you are a PR when you return to Canada.

If your PR card expired, you can renew your card. You still have your PR status even if your PR card expired.  You will only need the PR Card valid if you are traveling and are returning to Canada by plane, train, bus or boat.  If you are outside Canada, you can apply for a Permanent Resident Travel Document if your PR card is expired. If you are inside Canada and your PR card is expired, you can renew your PR Card.