How Flatten PDF works
PDF flatten merges all form fields and annotation appearances permanently into the page content, making them non-editable in any viewer. The result looks identical to the filled or annotated version, but the interactive layer is gone, the text you typed into fields, the checkboxes you ticked, the highlights you added all become fixed visual elements.
Flattening is the right step before archiving a completed form, sending a signed document, or preventing further edits to annotations. Unlike printing to PDF, it preserves the page's vector content and only removes the interactive layer, keeping the file compact and the text sharp. Flattening is irreversible, so keep a copy of the original if you might edit the fields again.