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SlimFile.app

Check a redacted PDF

Before you send a blacked-out document, find out whether the words underneath are really gone. The whole check runs in your browser — this file is never uploaded.

Choose your PDFs

up to 1 at a time.

PDFMax 25 MB each

How the check works, and what it cannot do

Each page is read twice: once for the text the file contains, and once as the picture you actually see. Where the file holds words that the picture does not show, those words are hidden rather than removed — which is exactly what a black box drawn over text looks like from the inside.

Read the result honestly. Finding something is strong evidence that the redaction failed. Finding nothing is not a guarantee: a scanned page has no text to check, an unusual font can defeat the comparison, and no automated test can prove a document is safe to publish. For anything that genuinely matters, redact the page properly and check the result by hand as well.

The first 40 pages are checked, which keeps a long document from locking up the browser.

How to use Check Redaction

  1. Add the PDF

    Up to 25 MB. Password-protected files are fine — you will be asked for the password once.

  2. It is checked in your browser

    Each page is read for the text it holds and rendered as the picture you see, then the two are compared. Nothing is uploaded.

  3. Read the report

    Anything hidden is listed with its page number, along with metadata, comments and attachments that no black box covers.

Why use SlimFile.app for this

  • Your file never leaves the browser

    The whole check runs on your machine — which matters, because the documents worth checking are the sensitive ones.

  • Shows you the words themselves

    Anything hidden is listed with its page number, exactly as it comes out of the file.

  • Free, no sign-up

    No account, no email address, no trial that runs out.

  • No watermark

    What you download is clean — nothing added to your file.

  • Never leaves your device

    This tool runs entirely in your browser. Your file is not uploaded anywhere.

Questions

How can text be in a PDF but not visible?
Because a black rectangle is a drawing, not an eraser. It is added on top of the page while the words stay underneath, so copying, searching or any text extractor brings them straight back.
Does finding nothing mean my PDF is safe?
No, and it is worth being clear about that. A scanned page has no text layer to check, an unusual font can defeat the comparison, and no automated test can prove a document is safe to publish. Finding something is strong evidence of a problem; finding nothing is not a guarantee.
Is my document uploaded anywhere?
No. The pages are read and rendered in your own browser, and nothing is sent to a server at any point.
What else does it look for?
The parts of a PDF that no black box covers: the document properties that name an author or a firm, comments left by reviewers, filled-in form fields, and files attached inside the PDF.

Read more

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