The main features I want are:

• Import PDFs and annotate them in the app’s native format (so that I’ll still be able to remove previous changes after I save and re-open it)
• Quickly add text boxes anywhere on the PDF
• Draw some basic shapes and lines with different colors (can either be notability-style “draw and hold to make shape” or just a classic “insert shapes” option from the toolbar)
• Have a page thumbnail option and can search text in the PDF file and quickly go there