FormFlatten

Guides & articles

Three long-form explainers on PDF form internals, flattening, and keeping your details off other people’s servers.

Hands filling in a ruled paper form held in a ring binder, pencil in hand

What is a PDF form? AcroForm vs XFA and why some forms won't open

A fillable PDF is an ordinary page with a second layer of objects on top. Here is what that layer contains, why the same file behaves differently in different readers, and what an XFA form is.

7 min read
A filled-in checklist on a clipboard stamped PASSED in red ink next to a rubber stamp

Why flatten a PDF form before sending it (and what flattening actually does)

Flattening turns your answers from editable field values into fixed page content. That changes how the file prints, how it merges, how it survives email — and it is irreversible.

6 min read
A person at a desk holding a pen above a sheet of handwritten notes

Filling official forms privately: keep your ID numbers off other people's servers

A tenancy application or a tax form carries more identifying data than most database breaches. Here is what happens when you upload one to a free online filler, and how to avoid it.

6 min read