I feel that the PDF editor could benefit from four features:
- More (customizable) colours;
Filter by annotation type and colour;
A general note tab in the left-hand column (integrated with the "notes" tab in PPP items ?). As an alternative, sticky notes, that will stay on despite the page, will do the job.
Marking by geometric shapes for non-OCR'd/wrongly OCR'd PDFs (I know this issue is available on standalone MetaPDF, so I guess it's just a matter of integrating it with PPP's editor).