What does it mean to flatten a PDF?
Flattening a PDF means merging interactive elements, such as form fields and their answers, comments, highlights and stamps, into the page content itself. The flattened PDF looks the same, but the fields can no longer be filled in or changed, and the comments become part of the page instead of separate, editable notes.
Also called: Flatten a PDF, Flattened PDF, Flatten form fields
Updated October 14, 2026 · By the PDFZyro team
Why flatten a PDF
A filled-in form keeps its answers in fields that anyone with a PDF editor can change. Flattening fixes the answers in place, which is useful when you send a completed application, a tax form or a contract. It also helps the document look the same everywhere: some apps, printers and phone viewers show form fields or comments differently, or not at all, while flattened content is simply part of the page.
Flattening comments and markup works the same way: highlights, notes, shapes and stamps become ordinary page content, so they print reliably and can't be moved or deleted by accident.
What flattening doesn't do
Flattening isn't security. The text that was in a field becomes page text, which can still be selected, copied and, with an editor, changed. It doesn't remove sensitive information either: for that you need redaction. And it doesn't lock the file: add a password to control who can open it, or a digital signature to show whether it has changed.
Flatten a copy, not your only file. Once a form is flattened you can't edit the answers, so keep the fillable version in case something needs correcting. If the document will be digitally signed, flatten it first: any change after signing breaks the signature.
Flattening by printing to PDF
Printing a PDF to a new PDF, sometimes called print to PDF, also flattens it, but it usually loses links, bookmarks and the document's structure, and it can lower the quality of pictures. A dedicated flatten option keeps the rest of the document as it is and only merges the fields or comments you choose.
How to flatten a PDF in PDFZyro
- To flatten a form, open it with Fill, fill it in and, when you finish, tick Flatten the form.
- To flatten comments and markup, open the document in Comment mode, open the more actions menu and choose Flatten annotations, for all pages or the pages you pick.
- The flattened PDF is saved as a new version, so the editable version stays in the document's history.
Tools and guides
- Guide: How to fill in a PDF formHow to fill in a PDF form: fillable, flat and scanned forms, step-by-step instructions, other free ways to do it, and what to check before you send it.
- Fill PDFFill in PDF forms, even flat ones without fields.
- Edit PDFChange text and pictures, add text, links and whiteout.
Related terms
- Fillable PDF form (AcroForm)A PDF with interactive fields you can type into, tick and sign in a PDF reader.
- RedactionPermanently removing sensitive text or images from a document before it is shared.
- Digital signatureA cryptographic, certificate-based seal that shows who signed a file and that it hasn't changed.