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This is a very detailed answer.

I want to know what if you get your PR, then get the PRTD to go abroad (study 1 year) and then come back and live in Canada for the next 4 years.

When will the person be questioned about their Residence Obligations? Once he is back after 1 year study or anytime they come back to the country or only at the end of the 5 years?

You don’t need any Canadian travel document to leave Canada. You need a PR card or PRTD to enter Canada by air.
 
This is a very detailed answer.

I want to know what if you get your PR, then get the PRTD to go abroad (study 1 year) and then come back and live in Canada for the next 4 years.

When will the person be questioned about their Residence Obligations? Once he is back after 1 year study or anytime they come back to the country or only at the end of the 5 years?

- You can't get a PRTD from within Canada. You can only apply for a PRTD once you are outside of Canada.
- You would only apply for a PRTD if you are outside of Canada, do not have a valid PR card, and want to return to Canada. If you have a valid PR card, then you would fly back to Canada using the valid PR card and no PRTD is required.
- Based on your scenario, no PRTD is needed. You would simply return on your PR card.
- You can be questioned about your Residency Obligation at any time.
 
It took me 1 month to get the approval, it also includes one interview by an officer on phone. It doesn’t include the time passport sent to embassy for visa stamping and receiving back. This process took another a week or 10 days

Hopefully someone here will see this to help. My husband is in the same situation at the moment. He had his application done August 8, did everything needed, got it approved and sent passport away. Was emailed today saying his application was dispatched to the IRCC for processing. We were hoping it'd be fast once it got to them. Will this add even longer times?