A PDF is not a picture of a document, it is the document: the text is real text that can be selected, copied and often edited, form fields still hold values, and annotations can be moved or deleted by whoever opens it. Flatten PDF redraws every page as an image and rebuilds them into a new PDF, so what the recipient gets looks identical but has nothing left to select, edit or fill in. It is the practical way to lock down a filled form or a signed document before sending it — and in Sensitive mode it happens entirely in your browser, which is the point when the document is a contract or an ID.
How to use Flatten PDF
- Choose your privacy mode. Sensitive flattens the document on your device; Normal uploads it to our sandboxed server for larger files.
- Drop in one PDF. Its pages appear as thumbnails so you can check you have the right document.
- Pick the detail level. Standard (144 DPI) suits most documents; Print (216 DPI) is worth it when the result will be printed or examined closely, and produces a larger file.
- Adjust quality if you need to. Lower values make a much smaller file at the cost of some sharpness in scanned or photographic pages.
- Click Process, then download. Every page is now a picture, laid out at exactly the size the original page had.
Worked example
A filled application form, locked before sending
You have completed a six-page PDF application form with interactive fields and signed the last page. Sent as-is, the recipient can click into every field and change the answers. Flattening it at Standard detail redraws each page — filled values, signature and all — as an image and rebuilds the six-page document at its original size. The result opens and prints identically, but the fields are gone: there is nothing to click into, nothing to retype, and no annotation to drag away. The trade is that the text is no longer selectable or searchable, and the file is usually larger than the original, because pictures of text cost more bytes than text.
Processing limits & specifications
| Mode | Location | Max file size | Retention |
|---|---|---|---|
| Sensitive mode | Your device (WASM) | Up to 75 MB (typical device) | Never stored / zero egress |
| Normal mode | Server sandbox | 300 MB | Deleted when you close the page |
Frequently asked questions
How do I make a PDF non-editable without uploading it?
Flatten it in Sensitive mode. Each page is rendered and reassembled by code running in your browser tab, so the document never reaches our servers — you can verify that in DevTools' Network tab while it runs.
Is this the same as password-protecting or redacting a PDF?
No, and the difference matters. Flattening removes the text layer, form fields and annotations, so there is nothing left to select or edit. It does not hide content that is visible on the page: if something is legible in the image, it is still legible. Drawing a black box over text and then flattening would remove the underlying text, but this tool is not a redaction tool and we do not describe it as one.
Is it free?
Yes — free, no signup, no email, no watermark.
Will the pages come out the right size?
Yes. Each flattened page is created at the original page's own size, so a document mixing A4 and landscape pages keeps that mix, and a page the original stored rotated comes out upright at the correct dimensions.
Why is the flattened file bigger than the original?
Because an image of a page needs more bytes than the instructions for drawing it. You can reduce that by lowering the detail level or the quality, and you can run the result through Compress PDF afterwards.
Can I still search the flattened document?
No. Searching needs a text layer and flattening removes it — that is exactly what makes the content uneditable. Keep the original if you need a searchable copy.