This is not the work permit document. It's a letter that let you continue working until a decision has been made. It's called "WP-EXT except PGWP".
IRCC recently is sending this (a couple of days after receiving the application) so that if you're employed or need an official letter, you can show this as a proof that you have applied and will receive your extension.
In IRCC website this is what has been posted:
After you apply online, we’ll send you a letter in your account (WP-EXT except PGWP) that you can use as proof that you’re authorized to keep working,
if you’re eligible.
- You can print this letter or show it with your current work permit.
- The letter is proof that you’re authorized to keep working under the same conditions as your original work permituntil we process your application.
- You can keep working past the expiry date on the letter until we process your application if the conditions are the same as on your original work permit.
Source:
https://www.canada.ca/en/immigration-refugees-citizenship/services/work-canada/permit/temporary/extend/after-apply.html
Processing time for WP is depend on the Processing Center workload. It can be between 3-4 months roughly.