It's recommended that you apply to extend your study permit at least 30 days before it expires. Remember, you must maintain a valid status if you intend to continue studying in Canada.

If you've applied for an extension before your permit expired, you have implied status until a decision is made on your application. You can continue studying and/or working in Canada under the same conditions as your existing permit until a decision is reached.

If you leave Canada while your extension is still being processed, you may not be allowed back into the country until your extension has been granted. It's advisable to remain in Canada while awaiting the decision.

If you change your program of study or educational institution, and the main reason for coming to Canada remains studying, it's not mandatory to get a new study permit. However, if you're moving from a program that doesn't have a work component to one that does (like a co-op), you'll need to apply for a co-op work permit.

Typically, you'll need a valid passport, a new letter of acceptance or a transcript from your school, proof of funds, and any other document required by IRCC. It's advisable to check the official IRCC website for the most up-to-date checklist.

If your extension is refused, you'll receive a refusal letter explaining the reason for the decision. Depending on the reason, you might consider re-applying with more robust evidence or consulting with an immigration advisor for further steps.

If you realize your permit has expired and you haven't applied for an extension, you have lost your student status in Canada. However, you can apply to restore your status within 90 days of your permit's expiration. During this restoration period, you cannot study or work.