How to mask data in a PDF
Masking a PDF means taking names, numbers and other personal details out of the file so nobody can read or copy them back. Covering them up isn't enough. Here's how to do it properly, for free, without uploading the document anywhere.
Open the PDF masking tool Free, no account. The file stays in your browser.The short version
- Open maskyourdocs and drop your PDF onto the page.
- Mark what should go: drag a box over it, or switch to Select text and sweep the words.
- To catch every copy of a name or number, type it into Find text and press Mask all.
- Press Export, then Generate. The masked PDF is checked automatically before you download it.
How to mask text in a PDF
Most PDFs made from Word, a bank portal or an e-signing service have a real text layer: you can select the words. That text is exactly what you need to get rid of, because it's what search, copy-paste and AI tools read.
- Open the PDF and choose Select text.
- Sweep across the words to mask. Each selection turns into a black bar straight away.
- Hover a bar to see what's under it, and remove it again if you got it wrong.
On export, every page you marked is rebuilt as an image with the bars burned in, so the original text isn't in the file any more. Pages you didn't touch are copied through as they were.
How to mask numbers in a PDF
Account numbers, card numbers, phone numbers, policy and customer IDs tend to repeat: in a header, in a table, again in a footer on page 12. Missing one is the most common way a masked document leaks.
- Type the number into Find text. The count shows how many times it appears across the whole PDF.
- Press Mask all to mark every occurrence at once.
- To keep part of a number visible, such as the last four digits, search for just the part you want hidden instead.
How to mask PII and personal details in a PDF
PII (personally identifiable information) is anything that points to a real person. Before sending or uploading a PDF, check it for:
- Full names, signatures and photos
- Home addresses, email addresses and phone numbers
- Dates of birth
- Bank, card, tax, passport, Aadhaar, PAN or social security numbers
- Medical details, employee IDs, salary figures
- QR codes and barcodes, which often encode the same details
Search for each name and number with Find text and Mask all, then use Draw box for anything that isn't text: signatures, photos, stamps and QR codes.
How to mask a scanned PDF or a photo of a document
A scan or a phone photo is just an image, so there's no text to select. Use Draw box and drag over each area. The same works for PNG, JPEG and HEIC files directly, and the exported image keeps its original resolution.
Why a black box over the text isn't enough
Drawing a rectangle or a black highlight in a PDF viewer adds a shape on top of the page. The text is still underneath: select it and paste it, open the file in another app, or hand it to an AI model, and it all comes back. Court filings and government reports have leaked this way for years.
Real masking (often called redaction) removes the content from the file. maskyourdocs flattens every masked page to an image, then reopens the finished PDF and searches it for each value you masked. If anything is still there, it tells you not to send the file.
Masking a PDF before you paste it into ChatGPT or Claude
If you're about to upload a contract, payslip, bank statement or medical letter to an AI chat, mask it first. Whatever you upload leaves your hands for good. A masked copy still gives the AI the context it needs, without the names and numbers.
Questions
Can I mask a PDF without Adobe Acrobat Pro?
Yes. maskyourdocs runs in any modern browser on Windows, macOS, Linux, Android or iOS. It's free, needs no account, and the PDF is never uploaded.
Does drawing a black rectangle mask a PDF?
Usually not. A shape or highlight added in a PDF viewer sits on top of the page, and the text underneath can still be selected, copied or extracted. Masking has to remove the text from the file itself.
Can I mask a scanned PDF?
Yes. A scan has no text layer, so use Draw box to cover each area. The masked pages are rebuilt from pixels, so whatever is under the box is gone.
Can I mask a password-protected PDF?
Yes, if you know the password. You're asked for it when the file opens, and everything after that works the same as for any other PDF.
Will the masked PDF still be searchable?
Pages you didn't mask are copied through unchanged and stay searchable. Pages you masked are flattened to an image, which is what guarantees the hidden text can't be recovered.