How PDF Editor works
PDF Editor lets you annotate any PDF with pdf-lib, add text boxes, drop in images, highlight passages with colour, and paint white-out boxes to cover content you want to hide. When you are done, download the result as a standard PDF you can share immediately.
The annotations are added as layers on top of the existing pages and burned into the output, so the source layout is preserved while your additions appear over it. White-out boxes make the covered area non-selectable in the downloaded file, though you should review the result before relying on it for sensitive redaction.