How to use it· 4 steps
- Drop the PDF into the box above. The tool counts its form fields, comments and links.
- Choose what to flatten: form fields, comments and markups, or both. Links are kept unless you ask for them to go.
- Press Flatten PDF and check the preview.
- Download the flattened copy, and keep the original if you might need to edit it again.
Step by step
How to use the flatten pdf
- 1Drop the PDF into the box above. The tool counts its form fields, comments and links.
- 2Choose what to flatten: form fields, comments and markups, or both. Links are kept unless you ask for them to go.
- 3Press Flatten PDF and check the preview.
- 4Download the flattened copy, and keep the original if you might need to edit it again.
What flattening actually does
Form fields and comments are not part of a PDF page. They are annotations: separate objects that sit on top of the page, each with its own small drawing — its appearance — that a viewer paints over the page when it shows it. A filled-in field, a yellow highlight and a “Approved” stamp all work this way, which is why they can be edited, moved, hidden or deleted independently of the page beneath.
Flattening takes each annotation's appearance and paints it into the page's own content, then deletes the annotation. Nothing visible changes. What changes is that the marks now belong to the page, like the text that was always there.
Placement follows the PDF specification's rule for appearances (ISO 32000-1, section 12.5.5), which maps each drawing's own box and transformation onto the annotation's rectangle. That detail matters: forms made in Acrobat for rotated pages store a rotation inside the appearance, and a flattener that simply drops the drawing at the rectangle's corner prints those fields sideways or out of place.
Why people flatten PDFs
To stop answers being changed. A completed application, a signed-off checklist or an invoice with filled fields can be edited by anyone with a form filler. Flattened, the values are page content, and changing them needs a PDF editor and leaves the edit far more obvious.
To make printing and viewing consistent. Whether annotations print depends on the viewer and its settings — Acrobat's print dialog, for example, can print a document with or without its markups — and some viewers, mobile apps and email previews do not draw form fields at all. Flattened content prints and displays everywhere, because it is just the page.
To fix fields that vanish or show the wrong value. A form saved with stale or missing field appearances relies on each viewer to redraw the fields from their values, and not every viewer does. Flattening redraws them once, properly, and bakes the result in. It also helps before merging or splitting: some tools drop form fields when they copy pages, and flattened answers survive any of them.
What is kept, and what is deliberately left alone
Links stay working by default, because a flattened document whose table of contents still jumps to its chapters is usually what you want. Tick the option to remove them if you need a completely inert file.
Redaction marks are never flattened. A redaction annotation is a proposal to remove content; painting its black box into the page would hide the text without removing it, and the words underneath would stay selectable and searchable. If you need content genuinely removed, use Redact PDF, which rebuilds the page so the characters are gone.
File attachments, sound, video and 3D annotations are also kept, because flattening them would keep only an icon and lose the thing it points to. A sticky note, on the other hand, is flattened into its icon — the note's text was never part of the page, so it does not survive. Copy anything important out of the notes first.
Before and after
Flattening cannot be undone, so keep the original. The flattened file is a new copy; the interactive version on your disk is untouched.
Hidden fields — values a form stores without showing them — are removed rather than painted, and their contents are dropped from the file instead of lingering as unreachable data. If the PDF was digitally signed, flattening changes it and the signature will report as invalid; the signature's visible appearance is kept on the page, its cryptographic proof is not.
Flattening is not security. The page can still be edited with a full PDF editor, and its text can be copied like any other. If the goal is to stop editing or copying, add a password with Protect PDF as well; if the goal is to hide information, flatten nothing and redact instead.
Answers
Frequently asked questions
Does flattening change how the PDF looks?
No. Each field and annotation is painted into the page from its own appearance, so the result looks the same — it just stops being interactive.
Can a flattened PDF be edited?
Not with a form filler or a comments panel, because the fields and comments are gone. A full PDF editor can still change page content, as it can with any PDF.
Will my links still work?
Yes, by default. Links are kept unless you tick Remove links too.
Does flattening redact text?
No, and redaction marks are deliberately left alone so they are never mistaken for removal. Use Redact PDF to actually remove text.
What happens to sticky notes?
The note's icon is painted into the page; the text inside the note is not, because it was never page content.
Is the file uploaded?
No. Flattening happens in your browser, and the original never leaves your device.