Flatten form fields draws the typed values into the page and removes the form, so the answers display everywhere and cannot be cleared. Flatten annotations draws each comment, highlight, stamp and freehand mark into the page exactly as the viewer showed it, then removes the annotation object, so the markup can no longer be moved, hidden or deleted. Links stay clickable unless you switch them off.
Flattening is one way. Keep the original if you may need to edit later, and sign after flattening, because a certificate signature applied before it will be invalidated.
The classic flattening moment is the form that arrives empty. Someone filled it in, attached it, and the recipient opened it in a reader that does not draw form values, or printed it from a browser that only prints the page layer. The answers were in the file the whole time, in a dictionary the reader ignored. Flattening ends that ambiguity by making the answers part of the page itself.
How to flatten a PDF
Add the PDF
A filled form, a marked-up document, or both. It is read into browser memory; nothing is uploaded.
Choose what to flatten
Form fields, comments and markup, or both, and whether links stay clickable. A file with no form only needs the annotations option, and the reverse.
Press Flatten PDF
Form values are drawn into each page's content with pdf-lib and the form dictionary is removed. With the annotations option on, each annotation's appearance is drawn into the page content and the annotation object is removed.
Download and check one page
Open the result and try to click a field. If nothing responds and the value is still visible, it worked.
They look the same on the page. They are simply no longer interactive.
There is nothing left to interpret differently. The page is the page.
The flattening runs in your browser. Filled forms often contain personal data, and it stays with you.
Why the layers cause trouble in the first place
A form value is not drawn on the page. It lives in a separate dictionary, and the reader is expected to render it on top using an appearance stream that may or may not have been written when the value was typed. Annotations work the same way. Whether they display, and how, depends on the software at the other end.
- Form values invisible in a browser previewMissing appearance streams
- Printed form comes out blankReader prints page layer only
- Comments missing on a colleague's phoneApp ignores annotations
- Recipient clears a field and retypes itForm still editable
- Archive system rejects the uploadInteractive layers not allowed
Flattening removes the question. The values and marks become ordinary page content, the same category as the printed text they sit beside, and every reader draws page content.
What each option does
Answers become ink
- Text fields, checkboxes, radio buttons and dropdowns are drawn onto the page
- The AcroForm dictionary is removed
- Values can no longer be cleared, retyped or tabbed through
- The file is no longer a fillable form, which is usually the point
Markup is removed
- Highlights, underlines, sticky notes, stamps and freehand marks are deleted from every page
- Link boxes and other annotation objects go with them
- Nothing is drawn into the page: the markup is gone, not frozen
- Right for a clean copy; wrong if reviewers' comments must stay visible
You can pick either or both. On a file that only has form fields, the annotations option does nothing, and vice versa. If the markup must remain visible to every reader rather than disappear, leave annotations on and run the file through Compress in Strong mode instead: it renders each page as the reader displays it, comments and highlights included, into a fixed image.
When to flatten, and when to hold off
- A form you have finished filling. Flatten before sending so the reviewer sees your answers and cannot alter them.
- A marked-up draft that should go out clean. Strip the reviewers' comments and highlights before the document leaves the team.
- Portal and archive uploads. Government portals and long-term archives often reject interactive layers. Flatten first. The archival pass does this alongside stripping encryption and metadata.
- Do not flatten a form still being filled. A template others complete must stay fillable. Flatten a copy once the answers are in.
- Do not flatten the only copy. There is no un-flatten. Keep the original.
What happens to file size
Usually the file shrinks slightly. The form dictionary goes, and so do any annotations you chose to remove, along with their appearance streams and pop-up definitions. The drawn form values are compact. Either way the change is small compared with the images and fonts that make up most of a PDF.
Why it runs in your browser
Filled forms are dense with personal data: names, addresses, dates of birth, account numbers, medical history, signatures. Uploading one to a server so the values can be drawn onto the page is a disproportionate exposure for a mechanical step.
The tool is right above
Everything on this page runs in your browser. Scroll up, drop the file, and keep it on your machine.
Common questions
The questions people ask with a filled form on screen.
01What does flattening a PDF do?
The form option draws typed values into the page content and removes the form, so the file looks the same everywhere but can no longer be edited through the fields. The annotations option removes comments, highlights and stamps from the file.
02Why would I flatten a form?
So the recipient sees your typed answers in every reader and on paper, and cannot clear or change them. Some viewers do not draw unflattened form values at all.
03Can I unflatten a PDF later?
No. Flattening is one-way. Keep the fillable original if you may need to change values later, and flatten a copy for each recipient.
04Does flattening remove signatures?
It invalidates certificate signatures, because it changes the file's bytes. A drawn signature image is ordinary page content and is unaffected. Sign after flattening, not before.
05Will the file get smaller?
Usually a little, because the form dictionary and any removed annotations are gone. The page content itself is unchanged.
06Do I need both options?
Only if the file has both form fields and markup you want gone. Turning on an option the file does not use is harmless. Keep annotations off if reviewers' comments must stay visible.
07Are my files uploaded anywhere?
No. The flattening runs in your browser and the file never leaves the device.
08Is it free?
Free. Every tool, unlimited use, no signup.