How PDF Forms Work (AcroForms)
The AcroForm standard (part of the PDF specification since version 1.2) defines a dictionary of form fields embedded in the PDF. Each field has a type, name, default value, and visual position. PDF viewers read this dictionary and render interactive widgets over the page.
Field Types
- Text field — single-line or multi-line text input
- Checkbox — boolean on/off
- Radio button group — single choice from mutually exclusive options
- Dropdown / combo box — select from a list of options
- List box — scrollable list, may allow multiple selections
- Signature field — placeholder for digital or drawn signatures
Saving a Filled Form
There are two ways to save a filled PDF:
- Save with fields intact — the form remains editable; values are stored in the annotation layer
- Save flattened — field values are baked into page content; the form is no longer editable
Send a flattened copy to recipients. Keep the unflattened version for your records if you need to update it later.
XFA Forms
Some PDFs use XFA (XML Forms Architecture) instead of AcroForms. XFA forms are Adobe-proprietary and not widely supported outside Acrobat. If a form shows only a blank page in most viewers, it's likely XFA. These require Acrobat or a dedicated XFA renderer.
Fill a PDF Form Now
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