Highlights lets you export your notes to a range of file formats and apps. To learn more about the different file formats and compatibility with third party apps see here.
1. Click the share icon in the toolbar
This brings up the export menu:
2. Select the destination you would like for your notes:
Save as files on disk:
Or send them directly to your favorite notes app:
To understand what information is included in the different file formats see here.
For free users of Highlights, PDF will be the only enabled option in the export menu. To get the full menu you need to unlock the Pro features first.