Yes, if you applied for a work permit extension before your work permit expired, you can keep working until a decision is made on your application.
You must stay in Canada and meet the conditions of your original work permit. For instance, if you have an employer-specific work permit, you must still work for the employer named on that permit.
We do not provide confirmation that you have implied status in Canada. However, you should keep proof that you submitted the application before your work permit expired. This includes copies of the application, the fee receipt, and something that confirms the date it was sent and delivered.