Thanks,Here you go,
Important information about using a representative:
A Use of Representative form (IMM 5476) must be submitted with an immigration application if the applicant used the services of a representative (such as an immigration consultant or lawyer) to help them prepare their application, or if the applicant wishes to appoint a representative (friend or family member) to conduct business on their behalf with IRCC.
If you appointed a representative and the IMM 5476 was correctly completed and signed, all correspondence from IRCC will be sent to the representative’s email or mailing address.
When submitting your PGP application:
If a paid or unpaid representative’s address was used as the mailing address for the sponsor or principal applicant on the application and a completed and signed IMM 5476 was not submitted; or
If a paid representative was appointed using a IMM5476 but is not in good standing; and/or
The IMM 5476 you submitted was not correctly completed and/or signed as required to appoint a paid or unpaid representative;
Then, all correspondence from IRCC will be sent to the sponsor or principal applicant’s email or mailing address on record as applicable. IRCC will not communicate with this representative until a correctly completed and signed IMM 5476 is received by IRCC.
I had the same PDF when I got AOR too, but I didn't send the REP. form, after 2 month which I called to change my address they told me this form is missing on my application, I use the webform and attached rep. form to it. better send it.
I think for sponsoring the parent there is two step, first confirmation of sponsoring, second PR application for parents, customer service on the phone told me this rep. form has 3 month valid, maybe because of that they ask to submit it again for PR application.
good luck