How to Flatten a PDF So Forms and Comments Can't Be Edited
Flatten a filled-in PDF form, comments and highlights into the page so nobody can change them. Learn when to flatten and how, free in your browser.
Quick answer
- Flattening turns form fields and annotations into ordinary page content: the PDF looks the same, but the answers and comments can't be edited.
- Open Flatten PDF, check the count of fields and annotations it found, choose what to flatten, then click Flatten & Download.
- Flattening can't be undone in the new file, so keep your editable original.
You've filled in a PDF form — a job application, a tax form, a rental agreement — and you're about to send it. Under the surface, every answer is still an editable field. Anyone who opens the file can change a figure or untick a box, and some phone apps and older readers show the fields blank. Flattening fixes both problems.
What does flattening a PDF do?
Form fields, sticky notes, highlights, stamps and drawings normally sit in a separate layer on top of the page. Flattening paints their current appearance onto the page itself and removes the interactive layer. The document looks the same, but what you see is now a fixed part of the page.
| Before flattening | After flattening |
|---|---|
| Form answers can be changed, cleared or retyped | Answers are fixed text on the page |
| Checkboxes and dropdowns can be clicked | They show the option that was chosen |
| Comments and highlights can be deleted or edited | The markup is part of the page |
| Some apps and printers skip the fields | Every app shows and prints the same thing |
How to flatten a PDF
- 1
Fill in and save the form first
Complete the form in your usual PDF reader, such as Adobe Acrobat Reader, Chrome, Edge or macOS Preview, and save it. Flattening locks in whatever the fields contain at that moment.
- 2
Open Flatten PDF
Go to Flatten PDF and add the file. PDFDoco counts its form fields and annotations, and lists what it found — for example 3 highlights and 2 sticky notes.
- 3
Choose what to flatten
Form fields and Annotations each have their own switch, and both start on. Turn one off to leave that layer editable — for example, to lock the form answers but keep review comments as comments.
- 4
Flatten and download
Click Flatten & Download. The new file's name ends in -flattened.pdf, and the results screen tells you how many fields and annotations were locked in.
See what will be locked in before you download — nothing is uploaded.
Flatten a PDFWhen should you flatten a PDF?
- Before sending a completed form. The recipient sees exactly what you entered, and it can't be changed by accident when they open it in a different app.
- Before printing. Some printers and print shops ignore form fields and leave blank spaces where your answers should be.
- At the end of a review. Flattening comments and highlights makes a fixed record of the feedback that every reader sees the same way.
- Before combining files. Lock in a filled-in form before merging it with other documents or removing pages, so the answers stay visible.
Good to know
- Links keep working. Hyperlinks aren't flattened, so they stay clickable.
- Already flat? If the PDF has no form fields or annotations, PDFDoco tells you there's nothing to lock in.
- A few annotations can't be flattened. Some, often sticky notes made by older software, are stored without a visible appearance, so there's nothing to paint onto the page. They're left as they are, and the results screen tells you how many.
- Text stays text. Flattening doesn't turn the page into a picture, so the content stays sharp and selectable.
- Digitally signed PDFs. Any change to a PDF with a certificate-based digital signature, including flattening, makes the signature show as invalid. Flatten before signing, not after.
- Password-protected PDFs need unlocking first with Unlock PDF.
Good to know: Flattening stops casual changes, not determined ones: someone with professional PDF editing software can still edit the page itself. To stop people opening the document at all, flatten it first and then add a password with Protect PDF. Our guide to password protecting a PDF explains how.
Tip: Save your editable original under a different name before you flatten. If a detail on the form changes later, you can update it and flatten again instead of filling it in from scratch.
Frequently asked questions
Can a flattened PDF be unflattened?
No. Once flattened, the fields and annotations no longer exist as separate objects, so ordinary PDF readers can't turn them back into editable fields. Keep your original if you might need to edit the form again.
Will my form answers still be readable and searchable?
Yes. Filled-in values become regular text on the page, so they look the same and can still be selected and searched.
Can I flatten only the comments and keep the form editable?
Yes. Turn off Form fields and leave Annotations on before you click Flatten & Download. You can also do the reverse.
Is my PDF uploaded when I flatten it?
No. Flatten PDF works inside your browser, so the file never leaves your device.