Flatten a PDF so nothing on it can be changed
A filled-in PDF form is still a form: anyone who opens it can click into a field and change your answers, and some viewers, printers and phone apps do not show the fields at all. Comments, highlights and stamps are similar — they float above the page as separate annotations. The Flatten PDF tool merges all of that into the page itself, so what you see is exactly what everyone else sees and prints.
Choose what to flatten: form fields, comments and annotations, or both. Web links can stay clickable. For the strongest lock, flatten every page into an image so the content can no longer be selected, copied or edited. A report lists exactly what was flattened and a preview shows the page content after flattening.
Everything is done in your browser. Signed contracts, tax forms and medical paperwork are never uploaded to a server.
How to flatten a PDF
- Drop your PDF onto the upload area. The tool lists the form fields, annotations and links it finds.
- Tick what to flatten: “Form fields”, “Comments and annotations”, or both. Keep “Keep web and page links clickable” on if the document has links readers should still use.
- For maximum protection, tick “Flatten everything to images” and choose a resolution — 150 DPI is a good balance.
- Press “Flatten PDF”, read the report and check the preview, then press “Download flattened PDF”.
Flatten PDF features
Form fields locked in
Text fields, checkboxes, radio buttons, dropdowns and list boxes are drawn onto the page exactly as filled, and the interactive form is removed.
Annotations burned in
Highlights, sticky notes, text boxes, stamps, shapes and ink drawings become part of the page content, with their colours and transparency.
Faithful placement
Each appearance is mapped from its bounding box onto its rectangle as the PDF specification describes, so rotated and scaled fields land in the right place.
Missing appearances rebuilt
Highlights, underlines, shapes, ink, sticky notes and text boxes saved without a visual appearance get one generated, so they don’t vanish.
Optional image flattening
Turn every page into an image at 100–300 DPI; links can still be re-created on top.
Clear report and preview
See how many fields and annotations were flattened, anything left alone and why, and the page content without any annotation layer.
Why people flatten PDFs
- Lock a filled form before sending it. Once flattened, your answers on an application, claim or tax form can’t be changed by accident — or on purpose — after you submit it.
- Make sure everyone sees the same thing. Phone viewers, browser previews and some printers ignore form fields or comments. Flattened content prints and displays everywhere.
- Fix comments that don’t print. Annotations without the “print” flag are skipped when printing; after flattening they are ordinary page content.
- Prepare for other tools. Merging, compressing or converting a PDF can drop form fields and comments. Flatten first with this tool, then use Merge PDF or Compress PDF to a Target Size.
Vector flattening or flattening to images?
The default mode keeps the PDF as text and vector graphics. Field values and annotations become drawing instructions in the page, so text stays sharp at any zoom and the file stays small, but someone with a full PDF editor could still edit the page content like any other PDF.
Flattening to images renders each page as a picture. Nothing can be selected or edited without retouching an image, which is the closest a PDF gets to a paper copy. The cost is a larger file and no text search; if you also need a small file, run the result through Compress PDF to a Target Size.
| Vector flattening | Flatten to images | |
|---|---|---|
| Fields and comments editable | No | No |
| Text selectable and searchable | Yes | No |
| Sharp at any zoom | Yes | Up to the chosen DPI |
| File size | About the same | Usually larger |
Good to know
Flattening changes the document, so an existing digital signature will show as invalid afterwards — flatten first and sign last with Sign PDF. Redaction marks that have not been applied are left alone, because drawing them would hide nothing; use Redact PDF to really remove content. Dynamic XFA forms keep their fields only in XFA data, which browsers can’t render, so they need Adobe Acrobat. To fill a form before flattening it, use Fill PDF Form; to stop editing without flattening, set permissions with Protect PDF.
Flatten PDF FAQ
What does it mean to flatten a PDF?
Flattening merges interactive or floating layers — form fields and annotations such as comments, highlights and stamps — into the page content. The PDF looks the same, but those items can no longer be clicked, edited or removed separately.
How do I flatten a fillable PDF form?
Fill it in first (for example with Fill PDF Form), then drop it here, keep “Form fields” ticked and press “Flatten PDF”. Your answers are drawn onto the page and the form fields are removed.
Will flattening change how my PDF looks?
No. Each field and annotation is drawn using its own appearance, at its own position, so the page looks as it did. The preview lets you confirm that before downloading.
Can a flattened PDF be unflattened?
Not from the flattened file — the fields and comments no longer exist as separate objects. Keep your original if you might need to edit it again.
Does flattening reduce the file size?
Vector flattening keeps the size about the same. Flattening to images usually makes it larger; compress it afterwards if you need a smaller file.
Is it safe to flatten confidential documents here?
Yes. The PDF is processed entirely in your browser and is never uploaded to a server.