Open the HTML or PDF article in the app's in‑app viewer, then open the list of all highlights for that article.
In the list of highlighted text cards, tap the ellipsis button located at the right side of the card to show the card options.
Tap the Share option to open your device's sharing sheet and send the highlighted text via any available platform (messaging apps, email, etc.).
To copy the highlighted text, tap the Copy option found between the Share and Delete options on the highlighted text card, then paste it into your desired messaging or note app.
Advisory: Always cite the source of a text.