What flattening a PDF does
Many PDFs have layers that sit on top of the page: form fields you can type into, sticky-note comments, highlights, stamps such as “Approved”, and freehand drawings. They are stored separately from the page content, which is why you can still edit or delete them. It is also why they sometimes vanish. Some viewers, printers and upload portals simply do not show them.
Flattening merges those layers into the page itself. The PDF looks exactly the same, but the answers and markups are now ordinary page content. Nobody can change a typed answer, untick a box or delete a comment, and every viewer shows the same thing.
Two ways to flatten
| Mode | What happens | Text stays selectable | Best for |
|---|---|---|---|
| Forms and comments | Each field and annotation is drawn into the page and the interactive layer is removed | Yes | Final copies of forms, reviewed drafts |
| Everything to images | Each page is rendered as a picture and rebuilt | No | Locking a document completely, odd forms that will not flatten cleanly |
Start with Forms and comments. It keeps the file small and the text searchable. Use Everything to images when you want a “photocopy” that nothing can unpick, or when a form uses characters the standard PDF font cannot draw (some Arabic, Urdu, Cyrillic or Chinese answers). The image mode captures exactly what you see on screen.
How to flatten a PDF
- Choose the PDF.
- Pick the mode. In Forms and comments you can flatten just the fields, just the comments, or both. Links are kept by default, because they are invisible and harmless.
- Click Flatten PDF. The tool reports how many fields and comments it flattened.
- Download the file, which ends in “-flattened”.
A worked example
You filled in a visa application in your PDF reader and the embassy’s portal rejects it with “form fields detected, please upload a flattened PDF”. Open it here, keep Forms and comments, and flatten. The tool reports “Flattened 37 form fields”. The new file looks identical, the answers are still crisp text, and the portal accepts it. If you also need it under the portal’s size limit, run it through Compress PDF next.
How it works
For form fields, the tool uses pdf-lib’s form flattening. Each field’s appearance (the picture of your answer that the PDF stores) is drawn into the page, and the field is removed. Fields with no stored appearance, which happens with some older form apps, first get a fresh one drawn from their value.
For comments and markups, the tool follows the method in the PDF specification. It takes each annotation’s appearance stream, works out the transformation that places it inside the annotation rectangle, draws it into the page and deletes the annotation. Hidden annotations are dropped and pop-up note windows are removed. A few apps store comments without any appearance and let each viewer draw them. Those cannot be flattened this way, and the tool tells you how many it left alone.
Everything happens in your browser. Your PDF is not uploaded anywhere.
Flattening is not redaction
Flattening fixes content in place. It does not remove anything that was already on the page underneath a comment or a white box. If you covered a name with a white rectangle annotation and flatten it, the name is still in the page’s text layer and can be copied. To remove information for good, use Redact PDF.
This tool vs typical online flatteners
| This tool | Typical online tools | |
|---|---|---|
| File uploaded | No | Yes |
| Choice of keeping text selectable | Yes | Often only “convert to image” |
| Reports what was flattened | Yes | Rarely |
| Limits or account | None | Common |
Related tools
Fill in a form first with Fill PDF Form, which can also flatten as it saves. Sign the final copy with Sign PDF, or lock it with a password using Protect PDF.