How to redact a PDF privately
If the point of redaction is that a name, an address or a medical line should not be seen, the worst first step is to send the whole file to a free online converter. Many of those services process the document on a server you do not control.
This page loads the PDF with PDF.js, lets you draw marks, and builds the download with pdf-lib, all in the browser. You can turn on airplane mode after the first load and it will still work. After you download the new file, open it and try to select the blacked-out words — you should get nothing. Also search the new file for a word you thought you had removed.
For a legal production, have a second person check every page. The free tool covers three pages and does not auto-find names or numbers; find-and-redact is on the paid waitlist. Acrobat Pro remains the office standard for large, reviewed productions.