BASALT · JOURNAL
How to redact a Social Security number from a PDF
An SSN can occur as 123-45-6789, 123456789, a partially masked value, or nine characters split across positioned PDF text objects. Redacting the one version you see is not a complete search.
Search every plausible form
Start with the exact number only in a controlled environment. Search the hyphenated and unhyphenated forms, spaced digits, the last four, and labels such as SSN, SS#, or Taxpayer ID. The label search finds poor OCR and numbers broken into separate text objects.
Review headers, footers, tables, and repeated account blocks. If the file is scanned, OCR it to make searching possible, but still inspect each page. OCR can confuse 0 with O, 1 with I, or omit a faint digit.
Remove both page representations
In a born-digital PDF, the number is usually text in a content stream. A black rectangle drawn above it is reversible because the characters remain. In a scan, the digits are pixels, often with an invisible OCR text layer beneath them. Safe redaction destroys the pixels and removes the matching OCR text.
Check AcroForm values separately. A tax or employment form may display an empty or masked field while the full value remains stored in the field dictionary. Flattening the visual appearance does not necessarily clear that stored value.
Look outside the page
Search document metadata, comments, attached source files, bookmarks, hidden layers, and earlier incremental revisions. A spreadsheet embedded in a PDF is not changed by page redaction. Inspecting a PDF before sharing lists the non-page carriers.
Export to a new file, reopen it with an independent parser, and search every form again. Copy the text around each redaction and verify that nearby names and labels survived.
Frequently asked questions
Is showing only the last four digits always permitted?
Not universally. Some filing rules use last four digits, while other policies require the entire number removed. Follow the rule controlling your disclosure.
Can OCR miss a Social Security number?
Yes. Degraded scans and character confusion are common. Search label words and inspect every page visually in addition to searching digit formats.
Is a black box enough to hide an SSN?
Only if the underlying text or image data is actually removed. A drawing annotation or rectangle alone leaves the number recoverable.
Doing it in Basalt
Basalt searches all pages, suggests SSN patterns on-device, removes text and image pixels with their OCR layer, strips hidden structures, and independently verifies the saved bytes. Nothing is uploaded. Download Basalt.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.