Flatten a PDF
Lock form fields and annotations into the page so nothing can be edited.
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Processed securely and deleted within the hour.
Two different operations
"Flatten" means two quite different things, and choosing the wrong one is the usual source of disappointment.
Flattening forms merges filled field values into the page content. The values stay visible and the text stays selectable and searchable, but the interactive fields are gone — so nobody can change what you entered. This is what people usually want when they have completed a form and are sending it on.
Rasterising everything renders each page to an image. Nothing remains editable, including the text, which is occasionally exactly the point and is usually a real loss — the document stops being searchable, copyable and accessible to screen readers, and the file typically grows.
Why flattening a form matters
A filled PDF form is still a form. The recipient can open it and change the figures, and the change leaves no trace. For anything that functions as a record — an application, a claim, a signed agreement — flattening turns entered values into fixed page content.
It also fixes a display problem: some readers show form fields blank or misaligned when the document is opened in software other than the one that filled it. Flattened values render identically everywhere.
Flattening is not protection
Worth saying plainly. Flattening stops casual editing; it is not encryption and it is not a signature. Anyone determined can still alter a PDF's content. If the document needs to be provably unaltered, that requires encryption or a cryptographic signature.
Annotations
Comments, highlights and stamps are merged into the page too, so they become part of the document rather than removable notes.
Common questions
Which mode should I use?
Forms in almost every case — it keeps the text selectable. Rasterising loses the text layer entirely.
Why flatten a filled form?
A filled form is still editable, and changes leave no trace. Flattening fixes the values into the page.
Does flattening protect the document?
It stops casual editing. It is not encryption and not a signature.
What happens to comments and highlights?
They are merged into the page and become part of the document.
Why does my form look blank in some readers?
Field appearances vary between readers. Flattened values render identically everywhere.