Flatten PDF
Local Processing (Offline Capable)Flatten PDF form fields into read-only page content so a filled form can't be edited after you share it. Processing runs entirely in your browser — free, no account, no upload; a file with no form fields comes back as a re-saved optimized copy.
How this tool works (no sign-up needed)
- Upload your file above. Each tool shows whether it runs Local (in your browser) or Cloud (encrypted servers).
- Adjust options, then click the Run / Convert / Process button.
- Wait for progress, then download the result. Use Next tools to continue.
If buttons are not visible, enable JavaScript — the interactive workspace loads in your browser.
Free · LocalMerge form fields into page content — read-only output
Supports application/pdf
Local — your file is processed in your browser and not uploaded to us. No account needed.
What is it?Flatten PDF is a PDFLean optimization tool: Merge form fields into read-only page content for tamper-proof distribution.
TL;DR: Merge form fields into read-only page content for tamper-proof distribution. Everything runs locally in your browser — free, no account, and your file is never uploaded; flattening is irreversible, so keep the unflattened original.
Measured: ~20 ms median on a typical sample — full benchmark table below.
Flattening merges interactive AcroForm fields into read-only page content, so a filled form can be shared without anyone editing the entries — the standard way to lock a filled form so it can't be edited. Processing runs entirely in your browser's memory: free, no account, no upload, files up to 10 MB. Two scopes: form fields only (default) or form fields plus annotations. Limits: flattening is irreversible — keep an unflattened copy; only AcroForm fields are merged, XFA is not flattened; existing digital signatures are invalidated; a file without form fields is returned as a re-saved optimized copy.
About this tool
Flattening is the final step before distributing a filled form: it bakes the entries into the page so recipients can view them but not change them. Scopes, file limits, and signature caveats are summarized in the facts above.
Measured performance benchmarks
| Sample | Input | Output | Median time | Size change |
|---|---|---|---|---|
| Flatten form fields (60-page report) | 160 KB | 158 KB | 20 ms | −1% |
Measured locally in your browser (isomorphic production code; samples are programmatically generated text PDFs, median of 5 runs). Real-world image-heavy PDFs differ — see the on-page limits.
How to use
Upload a PDF with form fields
Choose the flatten scope: form fields only, or form fields plus annotations
Click "Flatten PDF"
Download the read-only output
Watch: flatten a PDF in 77 seconds
Lock form fields and layers into the page so they can no longer be edited as separate elements. The video player loads only after you press play.
FAQ
What does flattening a PDF mean?
Flattening a PDF means converting its interactive form fields — text boxes, checkboxes, dropdowns — into ordinary page content. The filled-in values stay exactly as they appear, but the fields are removed, so nobody can click in and change an answer afterwards. Unlike Sanitize, flattening targets form fields only; scripts and metadata are left alone.
Should I keep an unflattened copy?
Yes. Flattening is irreversible: once the entries are baked into the page, no one — including you — can edit them as form fields again. Keep the original file whenever you might need to change the answers.
Will my file be uploaded?
No. Everything runs locally in your browser — your file is never uploaded, and closing the page clears it immediately.
Are there any limits?
Flattened forms cannot be edited again; single file size limit is ≤ 10MB (browser inline processing).
Will flattening affect digital signatures or XFA forms?
Flattening removes form field interactivity and invalidates existing digital signatures in signed documents. In addition, only AcroForm fields are merged into page content — XFA forms are not flattened.
Can I process multiple files in bulk?
A single tool page handles one task at a time; for bulk work use the Batch Processing workflow and add this tool as a step to run a whole set at once.
Is the processed file still editable?
The output is still a standard PDF that opens in any PDF reader; the original document is untouched and you receive a new file; however, flattened form content becomes read-only page elements and can no longer be filled as form fields.