How to properly redact a PDF?

You are right: drawing a black rectangle is not redaction. For a local, code-based solution, PyMuPDF supports actual PDF redaction without uploading the document.

The basic process is:

1. Work on a copy. Locate sensitive text with page.search_for() and mark the matching areas using page.add_redact_annot(). Mark image areas by coordinates too. Scanned text needs local OCR or manual review because ordinary text search will miss it.
2. Call page.apply_redactions() on each affected page. Adding the annotations alone does not remove content. Configure it to remove text, blank overlapping image pixels and remove overlapping vector graphics as appropriate.
3. Remove remaining comments, unwanted attachments and metadata. PyMuPDF provides methods such as delete_annot(), embfile_del(), set_metadata({}) and del_xml_metadata(). Those operations are not a universal sanitizer: forms, layers and other PDF structures need separate attention.
4. Save to a new file, using a full save with garbage collection, such as doc.save("redacted.pdf", garbage=4, deflate=True). Do not use an incremental save, which can retain earlier document data.

For a document with complex hidden content, a simpler security-focused option is to render the redacted pages to images and build a fresh PDF containing only those images. This avoids carrying over the original text objects, comments, forms, attachments and metadata. Rebuild from the rendered pages; merely flattening annotations or printing to PDF is not equivalent. The tradeoff is losing selectable text, accessibility information and interactive features.

Before sharing, reopen the new file and:

• Search for the removed names and addresses, and try selecting or copying around each redaction.
• Extract its text with a separate tool such as Poppler’s pdftotext.
• Inspect every page visually, including images and repeated occurrences.
• Check document properties, comments and attachments.

A failed text search alone is not proof of successful redaction—sensitive details may still be visible in images. For highly sensitive material, have someone else review the final output as well.