Flattening

Definition

Flattening takes the values held in interactive form fields and writes them into the page itself, then removes the fields. After flattening, the values are ordinary page content, so they appear in every PDF viewer — including the ones that ignore form fields entirely. The trade is one-directional: a flattened form can no longer be edited by filling, so the unflattened original has to be kept.

Example

A filled insurance claim form sent to a processor whose viewer renders the page but not the field layer. Unflattened, the processor sees empty boxes where the answers should be. Flattened, the answers are ink on the page and the form is readable in any software — but the sender keeps the editable copy because the claim might need correcting.

In the PDFLean tools

• flatten a PDF — the one-directional operation itself
• fill a PDF form — exports flattened by default for exactly this reason

Related reading

• Form Field — what the fields are before they are baked in
• PAdES — why signing usually comes after flattening decisions
• How to Create and Fill a PDF Form — where flattening sits in the sequence