To add to that, At least on fedora Linux and likely everywhere else Xournal can open PDF files and you can type free form text or even scribble from within the

To add to that, At least on fedora Linux and likely everywhere else Xournal can open PDF files and you can type free form text or even scribble from within the app. I use a pen because my Lenovo Flex 14 came with one but I imagine you could use a mouse pointer as well.