How to flatten a PDF (lock in form answers) in your browser
Bake a filled form's values into the page so the PDF can't be re-filled or edited, entirely in your browser with no upload.
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Flattening bakes a filled form's values into the page itself so the PDF can no longer be re-filled or edited — the standard way to lock in your answers before you send a form. AttachKit's Flatten tool does this entirely in your browser: the PDF never leaves your device.
Before you start
- What gets flattened: interactive (AcroForm) form fields — text boxes, checkboxes, dropdowns, and similar. Each field's value is drawn into the page content and the editable field itself is removed.
- What doesn't: sticky notes, highlights, and other markup annotations, as well as digital signatures, are out of scope for this tool — it targets form fields only.
- Password-protected PDFs can't be opened to flatten. Remove the password first with the Unlock tool, then come back.
- Flatten is free and needs no account. Because it runs 100% locally, your file stays on your device — you can open your browser's DevTools network tab and watch: no upload happens.
Steps
- Open Flatten a PDF.
- Drop your PDF onto the drop zone, or click it to pick a file. Loaded the wrong one? Click Choose another file.
- Click Flatten PDF. The button reads Flattening… while it works; processing happens on your device and usually takes a few seconds.
- Check the result panel (table below).
- Click Download flattened PDF. The copy is saved as
yourfile-flattened.pdf— your original file is untouched. - Optional: the download toast asks "Sign it next?" — click Fill it → to hand the flattened file straight to Fill in the same browser, again with no upload.
What the result panel means
| Panel | Meaning |
|---|---|
| Flattened N form fields | The values are now part of the page and can't be edited. |
| This PDF has no fillable form fields | There was nothing to flatten — a PDF without form fields is already "flat". |
Result
You get a copy of your PDF in which every form field's value is baked into the page. It looks identical in every PDF viewer, but the fields can no longer be clicked, changed, or re-filled. Document metadata (producer, creation date) is preserved rather than re-stamped.
If you need to change an answer later, flattening can't be undone on the flattened copy — go back to your original unflattened file, edit it in Fill, and flatten it again.
Related
- Flatten a PDF: troubleshooting
- Fill — fill a form before you flatten it
- Protect — add a password instead of (or after) flattening
- Unlock — remove a password so Flatten can open the file
Related
Still stuck? Contact support →