I love reading PDFs with GoodNotes on my tablet, because it is comfortable, and I can highlight and scribble notes.

Sometimes I'm reading a paper and it will keep referring to a figure on a previous page. I would love to temporarily lassoo that figure, and keep it as a floating window/overlay while I'm otherwise normally scrolling, reading, and marking the document.

Think of this as similar to the "Document split view" of some word processors, but much more flexible, and taking much less space away from the main document view.