Why can I still copy text under a black box in a PDF?

Because the box was drawn on top of the text without removing it. The text is still in the file, so selecting, searching or any extraction tool finds it. Proper redaction removes the content underneath.

Is redacted text in Kopitiam really gone?

Yes. Each page with a box is rebuilt as an image with the boxes painted in, so the original text on that page isn't in the new file. Kopitiam also checks the saved file and warns you if it finds any text inside a box.

Why can't I select text on the redacted page anymore?

Kopitiam removes the text by turning the whole redacted page into an image, so the remaining text on that page becomes part of the picture too. Pages without boxes keep their selectable text.

Can I undo a redaction?

Not in the downloaded file, which is the point. Before you press Redact & download, you can remove any box with its × button. Your original file is never changed, so keep it somewhere safe if you might need it.

Can I redact a scanned PDF?

Yes. Draw boxes over the parts of the scan you want hidden. Kopitiam paints them into a new image of the page, which also removes any invisible text layer the scanner added to that page.

How to redact a PDF properly (and why black boxes fail)

To redact a PDF properly, you need a tool that removes the content under the black box, not one that just draws the box on top. Then you check the saved file: try to select, copy and search for the redacted words. If nothing comes out, the redaction worked.

Drawing a black rectangle in an editor, or using a black highlighter, only changes what the page looks like. The text is still in the file, and anyone can copy it out in seconds. Courts, government departments and newspapers have all published documents this way by mistake. Here's why it happens, and how to avoid it.

Why a black box doesn't remove anything

A PDF page is a list of drawing instructions: put this text here, this line there, this photo in that corner. A black box is one more instruction, added on top. The text instruction underneath is untouched, so select-all and copy, a search, or any text extraction tool still finds the words.

The same goes for other ways people try to hide things:

Black highlight in Word, then export to PDF. The words export as normal text with a black background.
A white or matching-colour cover. Kopitiam's own Cover tool in Edit PDF works like this, which is right for fixing a typo and wrong for hiding a bank number.
A shape or sticker placed as a comment. Comments can be hidden, moved or deleted by whoever opens the file.
Cropping the page. A crop often only changes the visible area, and the cut-off part can still be in the file.

The test that settles it: open the saved file, drag across the black area, copy and paste into a note. Then search the file for a word you removed. If either finds anything, the text is still there.

How to redact a PDF with Kopitiam

Open Redact PDF and drop your file onto the page, or click to choose it. Every page is shown, labelled Page 1, Page 2 and so on.
Drag across each piece of text you want gone. A black box appears where you drag. The counter above the pages tells you how many boxes you've placed.
Drew one in the wrong place? Press the × on that box to remove it, then drag again.
Go through every page. There's no search-and-redact, so a name that appears on eight pages needs a box on each.
Press Redact & download. The new file saves as your file name with -redacted on the end. Your original file is not changed.
Read the note that appears. It should say no selectable text remains in any redacted area.

Make each box a little bigger than the words. Letters such as g, j and y hang below the line, and a box drawn tight can leave their tails showing. Very small drags, under a few pixels, are ignored, so a stray click won't add a box.

What Kopitiam actually does to your file

Each page that has at least one box is turned into a high-resolution image, with the black boxes painted into the pixels. The new page contains only that picture. The original text, fonts and any hidden layers on that page are not carried over, so there is nothing to select or extract.

Before the file is saved, Kopitiam reads back the pixels where each box should be, and stops with an error if any box isn't solid black where you drew it. After saving, it checks the new file for text inside your boxes. If any were found, you'd see a warning telling you not to treat the file as safely redacted.

This has a trade-off you should know about. On a redacted page, the rest of the text can no longer be selected or searched either, and links or form fields on that page stop working. Pages with no boxes are copied as they are, so they keep their selectable text. All of this happens in your browser, and the document is never uploaded.

What else can give your information away

Other pages. A name you removed from page 2 may still be in the footer of page 9, or in a table of contents.
Comments and notes on pages you didn't redact. Those pages are copied as they are, so a note on page 7 is still there.
Context. Removing a name but leaving the job title, the date and the branch can make the person easy to identify.
The file name. "Ahmad-salary-review.pdf" says a lot. Rename the file before you send it.
Document properties. Kopitiam builds a new file, so the original title and author fields aren't copied, but it's worth checking any file's properties in your PDF reader before sharing.

Scans, passwords, phones and long documents

Scanned documents. Many scanners add an invisible text layer so you can search the scan. A black box drawn in an ordinary editor leaves that layer behind. Kopitiam rebuilds each redacted page as a new image, so that page's hidden text layer goes too.
Password-protected PDFs. Kopitiam can't open locked files yet. Open it in your PDF reader with the password, use Print and then Save as PDF to make an unlocked copy, and redact that copy.
PDFs with editing restrictions. You'll see a message saying the tool can't change the file. The same Print to Save as PDF step makes a copy you can redact.
On a phone. Dragging on a page draws a box rather than scrolling, so place your finger carefully. A laptop is easier for documents with lots of small details to remove.
Long or large files. Redacted pages become images, so a file with many redacted pages gets bigger. If it's then too large to email, run it through Compress PDF. Every page is drawn in your browser first, so a very long scan can be slow on an older device.

Check the result before you send it

Open the downloaded file, not the one still on screen, in your usual PDF reader.
Drag across each black box and try to copy. Nothing should paste.
Use the reader's search for two or three words you removed.
For a thorough check, run the redacted file through PDF to Word & text and read the output. Removed words should not appear anywhere.
Scroll every page once, looking for anything you missed.

When Kopitiam isn't the right tool

Kopitiam suits everyday redaction: a bank statement for a visa application, a payslip for a tenancy, a passport scan with the number blacked out. It's not built for legal discovery or freedom of information work, where you may need to find every match of a word across hundreds of pages, stamp a reason code on each box, keep the rest of the page searchable, or keep a log of what was removed. Professional redaction software does those things.