"Fillable PDF" hides two very different technologies. AcroForms are simple, universal, and part of the PDF standard. XFA is powerful, dynamic, and increasingly broken outside Adobe Acrobat. Knowing which you're dealing with avoids hours of "why won't this open?" support tickets.
Form Field Types in AcroForms
| Field | Purpose | Notes |
|---|---|---|
| Text field | Free-form input | Supports formats: number, date, email, regex |
| Checkbox | Yes/no toggle | Custom export value per checkbox |
| Radio group | One-of-many choice | Same field name, different export values |
| List box | Visible scrollable choices | Single or multi-select |
| Combo box | Dropdown | Optionally editable for free text |
| Signature field | Cryptographic signing slot | Locks the document after signing |
AcroForms vs XFA — Which to Use
AcroForms are part of every PDF viewer ever shipped. They work in Acrobat, Chrome, Edge, Safari, macOS Preview, mobile readers, and every server-side PDF library. They cannot reflow layout, hide sections dynamically, or run complex JavaScript validations across pages.
XFA was created to address those limits — dynamic forms, repeating subforms, data-bound layout that grows with input. The trade-off is fragility. Adobe deprecated XFA support in PDF 2.0 (ISO 32000-2), and most non-Adobe viewers show blank pages or a warning. If your form must work for unknown recipients, ship AcroForms.
Designing a Good Fillable PDF
- Use clear field labels positioned consistently — top-left of each field for screen-reader order.
- Set tab order manually; never trust the auto-detected order on multi-column layouts.
- Add format validation (date, number, ZIP, email) so users get feedback before submitting.
- Mark required fields with both a visual indicator and the
Requiredflag. - Flatten finished forms before sending to print or archive.
Common Pitfalls
- Mixed AcroForm + XFA: some authoring tools save both — recipients see different content depending on viewer. Pick one.
- Tiny fields: if a field is shorter than its content, users see truncated text. Allow scroll or auto-shrink font.
- Calculation order: dependent fields recalculate in field order — reorder calculations explicitly when totals depend on subtotals.
PDF Form or Web Form?
Before building a PDF form, sanity-check that a PDF is the right container at all:
- Use a PDF form when the document must look identical in print, needs to be archived or signed as a fixed record, will be filled offline, or has to match an official paper layout (tax, government, HR onboarding).
- Use a web form when you mainly want to collect data at scale, validate it live, and drop it into a spreadsheet or database — web forms beat PDFs for aggregation and mobile UX.
- If you choose PDF, build it as a standard AcroForm, not XFA: AcroForms render in virtually every viewer including browsers, while XFA is Adobe-only and deprecated in PDF 2.0.
A common hybrid is a web form for intake that generates a flattened PDF record at the end — best of both worlds.
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