The way an article is added to the Library will at least in part determine how the user is able to find the article again later, to read it again or to cite it.
In our case this includes adding with full metadata (as made available from ACM Digital Library) and Visual-Meta stored additional metadata (manually, AI or AI with manual supervision added), including the annotations the user has made, since it can be useful to search based on something you know you highlighted for example.