Integrate WP with a premade site

Sorry if this is not the correct section, I looked around and couldn’t find a 100% fitting spot.

I have a website that has been running for a few years, but now I want to integrate into it using WP. My idea is to revamp most of the pages using WP’s themes.

Is this possible?

I’ve read: https://stackoverflow.com/questions/8615262/redirecting-old-htm-based-site-to-wordpress-permalinks and https://brassblogs.com/blog/make-your-existing-site-work-with-wordpress

But now I’m getting a bit stuck.

Thanks for the help in advance!