Lagging and slow performance Macbook M1 pro

Can someone explain me why my Macbook M1 pro 16 core CPU lags terribly after opening a file that my mate sent me. The file is 302 MB. He uses a mediocre 500 EUR Windows laptop and beats me in performance. What is going on and how can I fix this? It’s for a school project and it’s important that I can continue working without problems.