A lot of journal articles contain citations without web links. Highlights can lookup these citations and fetch the correct metadata right from the PDF.
1. Highlight, underline or strikethrough the citation in the PDF:
2. Tap the annotation to bring up the annotation popover
3. Select the Citation Lookup tool
Highlights will lookup the citation and fetch the metadata (if available):
Once complete, the marked up text in your notes will be replaced by a citation at the bottom of your notes:
Tapping the link will take you to the journals webpage for the article.
If you have previously opened a PDF with the cited metadata, there will also be a Highlights link to open the PDF directly: