PDFConvertersOnline.comHow to flatten a PDF
- Open the PDF. You'll see right away whether it has form fields or comments.
- Choose Form fields only, or Everything to turn each page into an image at 150 or 300 DPI.
- Press Flatten PDF and download the result.
What flattening means
A PDF can carry two kinds of content. The page itself holds the text, pictures and lines that were there from the start. On top of it sit interactive layers: form fields that can be typed into, and annotations such as comments, sticky notes, highlights, stamps and freehand drawings. Readers draw these layers separately, and each app handles them a little differently. Flattening merges them into the page, so what you see becomes ordinary page content that nobody can edit by clicking on it.
Why people flatten PDFs
- Sending a final version. A filled application or invoice shouldn't be changed after you send it. Flattening removes the editable fields.
- Answers that vanish. Some phone apps, printers and document portals ignore form fields or annotations, so a filled form shows up blank. Once flattened, the values are plain page content and appear everywhere.
- Uploading to picky systems. Some upload systems handle files with live form fields poorly; a flattened copy sidesteps the problem.
- Merging and printing. Forms with the same field names can clash when combined. Flatten each one first, then use Merge PDF.
The two modes compared
| Form fields only | Everything (image of each page) | |
|---|---|---|
| Form fields | Baked into the page | Baked into the page |
| Comments, highlights, stamps | Left as they are | Baked into the page |
| Text selectable and searchable | Yes | No, each page becomes a picture |
| File size | About the same | Usually larger, especially at 300 DPI |
Form fields only is the gentle option. It keeps the original page content untouched and only converts each field into the text or check mark it currently shows. Choose it whenever the file has fields and you don't need anything else locked.
Everything takes a picture of each page as it looks on screen, including every comment, stamp and drawing, and builds a new PDF from those pictures. Nothing interactive survives, and no hidden layer can be switched off later. The trade-off is that the text is no longer text: it can't be selected, copied or searched, and screen readers can't read it. At 150 DPI the pages look sharp on a screen and the file stays moderate; 300 DPI suits printing but can make the file several times bigger.
What flattening doesn't do
Flattening is not redaction. A white box or black bar that was added as an annotation becomes part of the picture in Everything mode, but in Form fields only mode the text underneath is still in the file. To remove confidential text reliably, use Redact PDF. Flattening also doesn't fill in blank fields for you: it freezes whatever values are there now, so fill them first with Fill PDF Form.
Done on your device
The PDF is processed by code inside this page. It isn't uploaded, so it works for tax forms and signed contracts that shouldn't leave your computer, and it keeps working even if your connection drops after the page has loaded.
Frequently asked questions
How do I know if my PDF has form fields?
Open it here. A message at the top of the workspace tells you how many form fields the file contains and whether it has comments or other markups.
Will my text still be selectable after flattening?
With Form fields only, yes. With Everything, no: each page is saved as an image, so the text can't be selected, copied or searched.
Why did my file get bigger?
Everything mode stores each page as a JPG picture, which is usually larger than the original text and vector graphics. Choose 150 DPI for a smaller file.
Can I undo flattening?
No. The fields and comments are gone from the flattened copy. Your original file isn't changed, so keep it if you may need to edit again.
Does flattening remove hidden information?
It doesn't clean out metadata or text hidden under shapes in Form fields only mode. For sensitive content use Redact PDF, and check the document properties with the PDF Metadata Editor.