Real Sociedad are a much better team in the Champions League compared to the La Liga this season. They completed Group D as leader despite having a competitive opponent like Inter in the same group. Can they be a challenging opponent for PSG as well? I think that they absolutely can. You can predict the reason behind that easily too in fact.

The reason why I think like that is PSG's inconsistent look in the tournament so far. As you have seen PSG barely managed to make it to this round thanks to the results of the last match week. If Newcastle won against Milan we were going to watch PSG in the Europa League.

Unless PSG perform the same as their recent Ligue 1 performances Real Sociedad can make things really difficult for them.
They can challenge PSG in the Champions League because we know that PSG did not have good records in this tournament, they mostly disappoint their fans when they put hope in them that is why every team is not always afraid of PSG because of the disappointments in several occasions in the Champions League.
Real Sociedad really tried very well in the Champions League this season as they were able to top their group which no one expected, I think they will try their best to eliminate PSG which I know will not be easy for them, but Sociedad's Champions League form this season is encouraging.
Real Sociedad having good season but sadly their attack is not effective which can help them in this knock out round because in last two games they fail to score any goal which is surely the worst thing for them even they top their group without any defeat, but now they needed aggressive approach which helps them for having better result and chance for the qualifying into next round which is not easy against team like PSG which is also improving their quality and performance after few poor results now things are looking much better and their chances are also high for the next round promotion even they are still not in favourite list, but they can make good mark with their performance.
Both teams can give better into their home leg match which will be give advantage for the jumping into next round in second leg match, mostly they will try to play with their tight defense which will give them better results as well.