What Does 'Flatten a PDF' Mean?

'Flatten' is a word you'll see in PDF tools without much explanation. Here's what it actually means and when it matters.

What flattening does

Flattening merges separate layers — like form fields, annotations, or a signature placed on top — into the page itself. After flattening, those elements become a fixed part of the page rather than editable objects.

Why people flatten

To stop form fields being edited, to make sure a signature or watermark can't be easily moved or removed, or to ensure the document looks identical everywhere it's opened.