My PC recently has been working really slow for some reason

Hi TechRepublic members!
I have an issue with my PC. Hope you will give me an advice.
I’ve been using Asus laptop for about a year for ordinary stuff (Internet, word etc) Recently, I’ve noticed my PC to work slower than usual.
I’ve downloaded a file about at that time. Do you think this could be an issue?
I’m looking for good advice on how to make my PC work as it was before.
Thank you!