Whether one is a permanent resident or not is determined by the provisions of the Immigration and Refugee Protection Act. While possession of a valid PR Card creates a presumption that a person is a permanent resident, it is not compulsory for a permanent resident to hold one. In fact, it is possible to hold a valid PR Card and at the same time face loss of permanent resident status due to not meeting residence obligations.
Similarly, it is possible to be a Canadian permanent resident and not hold a valid PR Card, although it may be more difficult to prove one's status.