Number 2 of your suggestions sounds like PDF markup, doesn't it? But maybe it's meant as a feature to be used not inside attachments (any external PDF editor can do that), but inside notes. Evernote has native capabilites of marking PDF; in Joplin you have to rely on the standard application for that format defined by your operating system. As it says in the yellow banner when you open a PDF: All changes you make will be saved to Joplin as changes to the note attachment.
