In a production web app I use Gotenberg. It’s definitely overkill for the task at hand, but if you find yourself doing this often I would highly recommend it. It’s dead easy to convert HTML (and I imagine XHTML) to PDF.
If when opened with a browser they have the right stylesheet, you can pirate m0nkrus' acrobat pro, then select all => right click => convert to pdf
Pretty sure calibre makes this easy if you don't wanna reinvent the wheel
came here to say calibre! it works and the converting is super simple. takes a little while for pdf files since its a big file but it works
Oh, I already have that installed. I'll try it.