JFDI Blog

Category: PDFs

  • How to redact a PDF properly (a black box isn’t enough)

    To redact a PDF properly, the hidden words have to be removed from the file, not just covered. A black rectangle, a black highlight or a white box drawn on top hides text from view, but the text is still there underneath, and anyone can select it, copy it and paste it somewhere else. Use a real redaction tool, then check the result before you send it.

    Redact a PDF

    The black box mistake keeps happening

    This isn’t a beginner’s error. It has caught out lawyers, government departments and newspapers for years:

    • January 2019: lawyers for Paul Manafort filed a document in his case with black bars over sensitive passages. A Guardian reporter found the text could be copied and pasted into a new document, revealing details about his contacts with Konstantin Kilimnik (Columbia Journalism Review).
    • 2014: redactions in a leaked CIA presentation published by The New York Times could be bypassed by highlighting and copying, exposing an NSA agent’s name.
    • 2011: a federal judge’s opinion in Apple v. Samsung had redacted passages that could be copied into a text document.
    • A 2011 study estimated that “thousands, and probably tens of thousands” of documents in the US federal courts’ PACER system had redaction failures.

    The last three are from the American Bar Association’s round-up of embarrassing redaction failures.

    Why covering doesn’t work

    A PDF isn’t a picture of a page. It’s a list of instructions: put these words here in this font, draw this shape there, place this image. When you draw a black box, you add one more instruction, draw a black rectangle, on top. The instruction that draws the words is untouched, so:

    • Copy and paste pulls the text from under the box.
    • Search finds it.
    • Screen readers read it aloud.
    • Text extraction by any program, including search engines, sees it.

    The same goes for black highlighting in Word before saving as PDF, and for white-out boxes.

    What proper redaction does

    Real redaction removes the content under the box from the file. In the JFDI PDF toolkit, the Redact tool works like this:

    1. Open the PDF in the toolkit and go to Edit & sign.
    2. Choose Redact (shortcut X) and drag over every name, number or passage that must go.
    3. Download. Each page with a redaction is rebuilt as a 200 dpi image with the black boxes burned in, so the hidden words no longer exist anywhere in the file.

    The trade-off: the rest of a redacted page can no longer be selected or searched, because the page is now a picture. Pages without redactions stay as normal text. Page numbers and watermarks are added afterwards, so they stay sharp.

    Nothing is uploaded at any point. The PDF is opened and rebuilt inside your browser, which is the point when the document is confidential.

    Don’t forget the hidden information

    Visible text isn’t the only thing that leaks. PDFs can carry:

    • Document details: the author’s name, the software used, creation and editing dates.
    • Editing history: some programs save changes by adding to the end of the file, so earlier versions of a page can still be inside.
    • Attachments, scripts and form data.
    • Text under scans: a scanned page that’s been through OCR has an invisible text layer behind the image.

    In the toolkit’s Finish tab, tick Remove hidden information before downloading. It strips the author, software, dates, embedded metadata, scripts, attachments and editing history. And check the file name: “Smith-v-Jones-settlement-£2.4m.pdf” can give away what the redactions hide.

    White-out or redact?

    White-outRedact
    Looks likeA white (or coloured) boxA black box
    The hidden wordsStill in the file. Anyone can copy them.Removed for good
    Rest of the pageUnchangedTurned into an image
    Use it forTidying up, hiding a typo, making space for new textNames, addresses, account numbers, anything confidential

    The toolkit’s Change existing text tool also covers the original words rather than removing them, so never use it to remove private information.

    Check before you send: five tests

    1. Select all and copy (Ctrl+A, Ctrl+C) on each redacted page, then paste into a text editor. Nothing hidden should appear.
    2. Search the PDF for a redacted word, such as a surname.
    3. Open it in a different PDF reader: your browser’s built-in viewer and one other.
    4. Check the document properties (File › Properties in most readers) for the author and title.
    5. Read the file name.

    Common questions

    Can a redaction be undone?

    Not when the content has been removed, as above. A drawn box can be “undone” by anyone with a PDF editor, by simply deleting the box.

    Is redacting a scanned document different?

    A scan is already a picture, so a black box burned into the image hides it. But scans often have an invisible OCR text layer; a real redaction tool removes that too, which is why the toolkit rebuilds the page.

    Does Adobe Acrobat do this properly?

    Yes, when you use its Redact tool and apply the redactions; drawing a black shape with its comment tools doesn’t. The same check above works for any tool.

    Related

  • How to compress a PDF to send by email

    To compress a PDF for email, shrink the pictures inside it: that’s where almost all the size is. Open it in the JFDI PDF toolkit, go to the Finish tab, choose Balanced (or Smallest for a tight limit) under Making the file smaller, and download. The new size is shown next to the old one. It’s free, there’s no upload, and there’s no file-size cap.

    Compress a PDF

    How big can an email attachment be?

    Email serviceLimitSource
    Gmail (personal)25 MB; anything bigger is sent as a Google Drive linkGoogle
    Outlook with an internet account such as Outlook.com20 MBMicrosoft
    Outlook with a work (Exchange) account10 MB by default; your IT team may have changed itMicrosoft

    Outlook’s limit covers the whole email, and the way attachments are encoded for sending can add up to a third to their size on some systems, so aim well under the limit. For a 10 MB limit, aim for 7 MB.

    Step by step

    1. Open the PDF toolkit and drop in your PDF, or choose Compress on the start page.
    2. Go to the Finish tab and find Making the file smaller.
    3. Choose a setting (see the table below). Start with Balanced.
    4. Download PDF. The message shows the new size beside the old one. If it’s still too big, try Small or Smallest.
    SettingPictures becomeGood for
    Keep as they areUnchangedText documents, or when quality matters most
    BalancedUp to 2,200 pixels, good-quality JPEGMost files: noticeably smaller, no visible loss on screen
    SmallUp to 1,500 pixelsSharing and reading on screen
    SmallestUp to 1,000 pixels, lower qualityEmail with a strict size limit

    Pictures are only replaced when the result is actually smaller. Unused data, including pages you deleted, is always removed.

    Why some PDFs barely shrink

    Compression works on pictures. A PDF that’s mostly text, such as a report exported from Word, is already compact: a page of text takes a few kilobytes, so there’s little to remove. If such a file is large, it’s usually because of:

    • Embedded fonts, especially several large ones. These can’t be removed without changing how the text looks.
    • Vector drawings such as detailed maps, plans or charts with thousands of points. For these, Turn every page into a picture (150 dpi) can help, but the text then can’t be selected, searched or read by screen readers.
    • Lots of pages. Split the document instead: the Finish tab can split a PDF into several files by page ranges.

    Scanned documents are the opposite: every page is a full-size photo, so they often shrink by most of their size.

    Other ways to get under the limit

    • Remove pages nobody needs, such as blank pages from a scanner, in the Pages tab.
    • Split the file into two emails with Splitting into several PDFs.
    • Scan at a lower resolution next time: 150 to 200 dpi is plenty for reading on screen.
    • Use a link instead of an attachment for very large files.

    Is it safe?

    The PDF is compressed inside your browser and never uploaded, so a payslip or a contract doesn’t pass through anyone’s server. If it’s confidential, add a password in the same Finish tab (AES-256 encryption) and send the password by a different route.

    Related

  • How to sign a PDF for free, with no account

    To sign a PDF for free, open it in the JFDI PDF toolkit, choose Signature, then draw, type or upload your signature and drag it into place. Download the signed PDF. There’s no account, no watermark and no limit on how many documents you sign, and the document stays on your device the whole time.

    Sign a PDF

    Step by step

    1. Open the PDF toolkit and drop your PDF on the page, or choose Sign a PDF on the start page.
    2. Go to the page that needs signing and choose Signature (shortcut S).
    3. Make your signature in one of three ways:
      • Draw with a mouse, trackpad, finger or stylus (pen pressure is used where your device supports it). Choose black or one of two blues.
      • Type your name and pick a handwriting style.
      • Upload a photo or scan of your signature on paper. Remove the white background makes the paper see-through, so only the ink shows.
    4. Drag it into place and resize it from the corners.
    5. Add the date with the Date tool, which stamps today’s date as text you can edit. Use Add text for your printed name or initials.
    6. Download PDF.

    Tick Remember on this device to reuse your signature next time. It’s kept in your browser only, never on a server, and you can delete it with its ×.

    Which signature method looks best?

    MethodLooks likeBest for
    Upload a photoYour real ink signatureContracts and anything formal
    DrawClose to real, if you have a stylus or a steady fingerQuick forms on a phone or tablet
    TypeA neat handwriting fontInformal approvals, where a signature is a formality

    For a photo, sign in black pen on plain white paper, photograph it in good light, and crop close. The background removal does the rest.

    Is this a legally valid signature?

    What you’re adding is an electronic signature: a picture of your signature placed on the page. In the UK, EU and US, electronic signatures are generally accepted for everyday paperwork such as tenancy agreements, consent forms, job offers and invoices. Some documents have special rules, such as wills and some property deeds, and some organisations insist on a particular service. If the stakes are high, check with whoever asked you to sign.

    It isn’t a certificate-based digital signature, the kind that cryptographically locks a document and proves who signed it. If a PDF already carries one of those, changing the file in any way, in this or any other editor, makes that signature show as no longer valid.

    Filling in the rest of the form

    Most documents that need signing also need filling in:

    • Fillable forms show blue-tinted boxes in the editor. Click a box and type, tick checkboxes and pick from drop-downs with the Select tool. Answers stay editable after download unless you tick Lock form answers in place in the Finish tab.
    • Forms with no boxes, such as scans, can be filled in with Add text, Tick and Date.

    Sending it back

    If the signed file is too big to email, the Finish tab’s Making the file smaller setting usually fixes that; see how to compress a PDF for email. If it’s confidential, you can add a password there too, encrypted with AES-256. Send the password separately, by text or phone.

    Why not use a free e-signature service?

    Signature services are built for collecting signatures from other people, with tracking and reminders, and they’re good at that. But they need accounts, usually limit free use, and keep your document on their servers. To sign something yourself and send it back, you don’t need any of that.

    Related

  • How to edit a PDF without uploading it

    To edit a PDF without uploading it, use an editor that runs inside your browser rather than on a company’s server. The JFDI PDF toolkit opens the file on your device, lets you add and change text, sign, fill in forms, reorder pages and redact, then rebuilds the PDF locally when you download. The file never leaves your computer, and there’s no account.

    Edit a PDF

    Why it matters

    The PDFs people edit are often the most sensitive files they have: contracts, payslips, tax forms, medical letters, ID scans. Most popular online editors upload them to process them. Their privacy pages say so, and say how long the files are kept, typically from one hour to a day. That may be fine for a menu; it’s worth avoiding for a tenancy agreement. We looked at what six well-known tools say in Which online file tools upload your files?

    What you can do

    TaskHow
    Add text anywhereAdd text (T): click and type
    Change a line of existing textChange existing text (E): click the line and retype
    SignSignature (S): draw, type or upload your signature
    Fill in a formClick the blue-tinted boxes with Select (V)
    Tick boxes on a form with no fieldsTick and Cross tools
    Highlight, draw, add shapes and arrowsHighlight (H), Draw (D), Rectangle (R), Arrow (A)
    Add a picture or logoImage
    Hide something for goodRedact (X)
    Reorder, rotate, delete or duplicate pagesPages tab
    Merge several PDFsOpen them together; their pages appear in one list
    Add page numbers, a header, footer or watermarkFinish tab
    Make the file smaller, or add a passwordFinish tab

    Everything can be undone with Ctrl+Z (⌘+Z on a Mac).

    Step by step: changing a line of text

    1. Open the PDF toolkit and drop your PDF on the page.
    2. Go to Edit & sign and choose Change existing text (shortcut E). Lines of the PDF’s own text light up as you point at them.
    3. Click the line you want to change and type the new words. The toolkit matches the position, size, colour and style (sans-serif, serif or monospaced) as closely as it can.
    4. Download PDF from the top right.

    What you can’t do (with any editor, mostly)

    PDFs aren’t word-processor documents, and it helps to know the limits:

    • Changed text is laid over the original. The tool covers the old line with a box in the background colour and puts the new text on top. That’s how most PDF editors work behind the scenes, but it means the original words are still in the file. Never use it to remove private information: use Redact.
    • Fonts are matched, not copied. New text uses Helvetica, Times or Courier, the fonts every PDF reader has. Unless the original used one of those, look closely and pick the nearest.
    • Paragraphs don’t reflow. Change a line and the next line doesn’t move up or down. For big rewrites, go back to the original Word or Pages file if you have it.
    • Scanned pages are pictures. There’s no text to change. Use White-out to cover the old words and Add text for the new ones.

    How to check nothing is uploaded

    You don’t have to take our word for it. In Chrome, Edge or Firefox, press F12 to open the developer tools and choose the Network tab. Open and edit your PDF, then download it. You’ll see the page’s own files load, and nothing sent out containing your document. Our guide to checking whether a website uploads your file shows what to look for.

    Common questions

    Is there a file size or page limit?

    No set limit. Everything happens on your device, so very large files depend on its memory. Computers cope with big files much better than phones.

    Does it work on a phone or tablet?

    Yes. The tools scroll along the top, and you can sign with your finger.

    Is my work saved if I close the tab?

    No, because nothing is stored anywhere. Your browser asks you to confirm if you try to close the tab with changes you haven’t downloaded.

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