This is standard procedure and legal in many airlines, including perhaps PIA. The only reason this should be the subject of a thread on Pprune is to show how often the Press makes a scandal out of nothing......
The Regulations in Canada:
https://www.tc.gc.ca/eng/civilaviati...s-720-2153.htm
2) Where the flight is conducted under Subpart 4 or 5 of Part VII of the Canadian Aviation Regulations using an aircraft other than a helicopter, and the flight crew is augmented by the addition of at least one fully qualified flight crew member, flight duty time may be extended to 15 consecutive hours if:
(amended 1998/03/23)
(a) the additional flight crew member occupies a flight deck observer seat during take-offs and landings unless the observer seat is required by an air carrier inspector, in which case, a passenger seat must be available for the flight crew member; and
(amended 1998/03/23)
(b) the subsequent minimum rest period is increased by at least 2 hours.
(amended 1998/03/23)
(3) Where a flight crew is augmented by the addition of at least one flight crew member, the division of duty and rest is balanced between the flight crew members and a flight relief facility is provided, flight duty time may be extended if:
(a) where a flight relief facility - seat is provided, the flight duty time may be extended to 17 consecutive hours, in which case the maximum flight deck duty time for any flight crew member shall be 12 hours;
(b) where a flight relief facility - bunk is provided, the flight duty time may be extended to 20 consecutive hours, in which case the maximum flight deck duty time for any flight crew member shall be 14 hours;
(c) the subsequent minimum rest period shall be at least equal to the length of the preceding flight duty time; and
(d) a maximum of 3 sectors may be completed.