Xournal++ is useful when a sketch, equation or handwritten explanation is clearer than a typed comment. Preserve the native note file for editing and use PDF exports for recipients who only need to read the finished notes.
Import a PDF as a background and keep handwritten explanation on separate layers when that makes review easier. Save the native note file as the editable master, then export a PDF for sharing. Test pen pressure and eraser behavior before using the app in a live session.