How to Flatten a PDF Form
Flattening a PDF form converts interactive, fillable form fields into permanent, non-editable content, essentially freezing whatever was entered into those fields so they behave like regular static text on the page from then on.
Why you'd want to flatten a form
Once a form has been filled out and is ready to submit, share, or archive, flattening it prevents the recipient (or you, accidentally) from changing the entered answers later. It also improves compatibility, since some PDF viewers don't render fillable form fields consistently, but they all render flattened static content the same way.
What happens to the data during flattening
The values entered into each field get 'baked' into the page as regular text or graphics, permanently replacing the interactive field. This is a one-way operation: once flattened, the form fields are gone, and you can't go back and edit individual answers the way you could before flattening, short of manually editing the text like any other PDF content.
When not to flatten yet
If a form still needs additional people to fill in more fields, like a multi-signer approval form, don't flatten it until everyone is done, since flattening removes the very fields the next person would need to fill in.
Flattening as part of archiving
Flattening is a common last step before archiving completed forms long-term, since a flattened PDF is simpler, more universally compatible, and immune to any accidental edits to what should be a finalized historical record.
