You need to get it from where you were married in Pakistan. From the IRCC checklist
For marriages which took place in Pakistan: The marriage certificate to be submitted is the “Nikkah Nama”. It must bear the Nikkah registry seal as evidence that the marriage has been properly registered by the union council or the relevant government authority in the relevant region. The NADRA (National Database and Registration Authority) issued marriage certificate should be included but is not sufficient evidence on its own.