Based on history, PSG's performance was really poor during knockout stage, they only very strong during group stage.
Why I say so is because Real Sociedad they don't have any good attacker that can hold their forward very well, secondly they don't have good midfielders compared to PSG.
Based on history PSG performance was not that poor at knockout stage and i believe they are strong in both stage.
In the Champions League, everything is possible and with the current form of Paris Saint Germain they also still have weaknesses that can be exploited, so they are still very beatable. The truth is that Paris Saint Germain have a poor record in the Champions League, and of course for a club of their size that is something very unsatisfactory. Almost every season they try to win the title but every season they always get repeated failures.
They lose every season, but they lose to tough teams. I can not say that Real Sociedad is a weak team, but certainly not at the level of PSG, so the Parisians have every chance to pass in 1/4, although I do not think they can go further, because this season there are many strong teams, but I think that 1/8 will not give them trouble