May 6, 2026 · Flatten PDF
How To Flatten A PDF - Lock Down Form Fields And Annotations
A filled PDF form is still editable. The recipient can change the values, the dates, the dollar amounts - and unless they're trying to be honest, you may never know.
Flatten PDF freezes the form. Field values become permanent page content. Annotations become part of the page. The file looks the same but is no longer editable in the way that matters.
Why Flatten
Flattening is what you do before sending a filled-out form. Tax forms, expense reports, signed contracts, scanned signatures - anywhere the values need to stick.
It's also what you do before printing to a printer that doesn't render PDF annotations correctly. Some industrial and large-format printers strip annotations; flattening converts them to page content the printer will faithfully reproduce.
What Happens To Comments And Highlights
Page-level annotations are stripped during flattening. If you want comments preserved visually, print the PDF to PDF first (using your OS's print dialog) - that bakes the annotations as page content - then run Flatten on the result.
Form field values, in contrast, are always baked in. A user who fills out a form, then runs Flatten, will get a PDF where the answers are part of the page.
How To Flatten
Open Flatten PDF. Drop in the filled or annotated PDF. Click Flatten. Download the result.
There is no undo. Keep your original file if you might need to edit the form values later.
Privacy
Flattening runs in your browser. The PDF never leaves your device.
Lock down a filled form before sending with Flatten PDF. Free, in your browser.