Prevent text extraction under highlight / annotation

I need to hide parts of the document and avoid the possibility of copying the text under the hidden areas.
How to prevent text extraction from a PDF form under highlight text or under a annotations?


PDFTron for angular

Generally speaking you cannot prevent someone from extracting content from a PDF file. Ideally the content is simply removed.

Does the user ever get full access (download) to the PDF?
If not, you control the full interactive experience (e.g. viewer)?
Can you just delete/remove the content under the annotation?
Do you have an example PDF with the annotation over the content to prevent extraction of?