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Free · runs in your browser · the PDF is never uploaded

Is your PDF leaking? Check it for hidden data

Short answer

Drop the PDF into the checker below. In a few seconds it tells you whether the file contains text under black boxes (a failed redaction), text you can’t see (white, tiny or off the page), personal data such as emails, phone and card numbers, document properties like an author name, attachments or filled-in form fields, and scripts. Each problem comes with a button to the tool that fixes it. It all runs in your browser, so the file is never uploaded.

Loading checker…

What the checker looks for

PDFs leak in predictable ways. Most of them come down to the same mistake: something is hidden from view but still in the file. These are the six things the checker looks at:

Text under black boxes
A black rectangle drawn over text hides it from your eyes, not from the file. The checker renders each page and finds text whose area is covered by a solid dark shape. Anyone could select and copy that text.
Hidden text
Text coloured white, shrunk to a fraction of a point, covered by a white shape or placed outside the page edge. It doesn’t show on screen but it’s in search results and copy-paste.
Personal information
Email addresses, US and international phone numbers, card numbers that pass a checksum, IBANs, US Social Security numbers and Aadhaar- and PAN-style IDs, found in the document’s text. Values are shown masked.
Document properties
Author, title, subject and keywords in the file’s properties, plus any author names in the XMP metadata block. These travel with the file without appearing on any page.
Attachments and form data
Whole files embedded inside the PDF, and form fields that still hold what someone typed into them.
Scripts and auto-actions
JavaScript, launch actions and form-submit actions, plus actions that run when the file opens. Rare in everyday documents and worth removing before sharing.

How to check a PDF before you share it

  1. 1

    Drop the PDF you’re about to send into the checker above, or tap to choose it.

  2. 2

    Wait a few seconds while each page is read and rendered in your browser. Long documents take longer.

  3. 3

    Read the verdict: Leaking means something can expose content you meant to hide; Review means there’s personal data or metadata to double-check; No leaks found means none of the checks found anything.

  4. 4

    For each problem, press the fix button. The tool opens with the same file ready to continue.

  5. 5

    Run the check again on the fixed file before you send it.

How the black-box check works

Most tools that look for hidden text read the file’s drawing instructions and try to work out what overlaps what. That breaks easily, because there are dozens of ways to draw a black box. This checker looks at the result instead.

It renders each page as an image, exactly as a viewer would show it, then looks at the pixels where each piece of text is supposed to be. Visible text always makes a mix of colours: dark letters on a light background, or light letters on a dark one. If the area is a single flat colour, the text isn’t visible. Flat and dark means it’s under a black box. Flat and light means it’s white, or covered by a white shape.

This catches boxes drawn with shape tools and with most comment and highlighter tools. To remove the text for real, use Redact, which deletes what’s under the box. The redaction guide explains the difference.

What it can’t catch

  • Text checks only work where the PDF has a text layer. Scanned pages need OCR first.
  • Rotated text is skipped by the covered-text check.
  • Personal-data detection covers the formats listed above. Names, addresses and local phone numbers written without a country code can be missed.
  • Text hidden behind a photo or other image isn’t detected; only solid, flat shapes are.
  • Script detection looks for known markers and can miss ones hidden inside compressed parts of the file.
  • Password-protected PDFs have to be unlocked first.

Frequently asked questions

  • How can I tell if a redacted PDF is really redacted?
    Drop it into the checker. If text is still sitting under the black boxes, it shows up under Text under black boxes with the page number. You can also drag your cursor across a black bar in any PDF viewer: if text highlights, the redaction failed.
  • Is my PDF uploaded when I check it?
    No. The checker runs entirely in your browser tab. The file is read and rendered on your device and never sent to a server.
  • Can it check scanned PDFs?
    Partly. A scan has no text layer, so the text checks have nothing to read; the checker tells you when that happens. Metadata, attachments and scripts are still checked. Run OCR first to check the scanned text.
  • Does a clean result mean the PDF is safe to share?
    It means none of these problems were detected. It can’t tell whether a name or a paragraph is confidential, and it doesn’t find personal data written in unusual formats. Read the document once yourself before sending it.
  • What does the shareable summary contain?
    Only the verdict and the number of findings in each category. It never includes the file name or any text from the document.
  • How do I fix text hidden under a black box?
    Open Redact and draw a box over the same area again, then apply. Redact rebuilds each page that has a box as an image with the black areas burned in, so the text underneath is no longer in the file.

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Written by Sumit · Last reviewed 12 Oct 2026