On iOS11, can I highlight PDFs and make notes with my finger? I've seen a number of reviews that show the functionality of being able to highlight PDFs on iOS11 using the Apple Pencil, however, I'm wondering if I can do this with my finger on the normal (non-pro) iPad?
Yes. iOS 11 allows markup with finger of PDF’s opened in the Files App or previewed. Works on iPad and iPhone.  No need for a pencil unless one needs finer control of drawing. 

The example below is a markup of a webpage that was saved as a PDF using my finger.