Hi,
What are you referring to when you wrote about "shipping docs"?
In my case I was getting them shipped from Canada to USA. I had prepared the shipping label in Fedex. I also prepared the Commercial Invoice (which can be done while preparing the shipment on Fedex website). Once I had all of these, I emailed electronic copies of the same to my contact in Canada and they were able to just take a printout of these and ship.
For people in the US, this process is familiar because after PPR, we are (typically) required to send passports to Canada Ottawa CPC, and not Local Visa Office. And sending them involves including an envelop with return labels.
In case of PR cards, all I had to do was generate the return labels.
Regarding the commercial invoice, people in the US are experiencing issues in the return process if they do not have a commercial invoice. It seems, sometimes the package gets held up by US Customs since they are not sure what is in the package. Having a commercial invoice helps avoid that. I'm not sure if this is 100% certain info but many people know about this and some recommend the same.
The commercial invoice itself was not a big deal, since I just declared that the package contains immigration documents with commercial value of $1 (commercial value has to be greater than 0 for Fedex website to generate commercial invoice).
Both the times (when getting passports back with CoPR, and when getting PR Cards), I had no issues with US customs.
Hope this helps
-S.