Static and dynamic forms

XFA defines static forms (since XFA 2.0 and before) and dynamic forms (since XFA 2.1 or 2.2).

In a static form the form’s appearance and layout is fixed, regardless of the field content. Any unfilled fields are present in the form. By default, static forms do not require re-rendering. XFA recognises two types of static forms: "old-style static forms" (using "full XFA") and XFAF (a subset of full XFA, defined since XFA 2.5).

Dynamic forms (defined since XFA 2.1 or 2.2) can change in appearance in several ways in response to changes in the data. Dynamic form requires rendering of its content on file opening. Dynamic forms may also be designed to change structure to accommodate changes in the structure of the data supplied to the form. For example, a page of a form may be omitted if there is no data for it. Another example is a field that may occupy a variable amount of space on the page, resizing itself to efficiently hold its content. Dynamic form cannot rely on a PDF representation of its boilerplate, because the positioning and layout of the boilerplate change as the fields grow and shrink or as subforms are omitted and included.

Profiles

Starting with XFA 2.5 forms can use a subset of the full XFA capability. Currently the only specified is the XFAF profile.

XFA can be used as:

• full XFA - which express all of the form, including boilerplate, directly in XFA (without any PDF or without a complete PDF background). It can be packaged inside a "shell PDF" with minimal PDF markup or as a standalone XDP. It is used for dynamic XFA forms (since XFA 2.1) and also for so called "traditional" (old-style) static XFA forms. Optionally it may include a pre-rendered depiction of the XFA form as PDF pages - but it is useful only for traditional static forms. Dynamic XFA must be rendered on file opening.
• XFAF (XFA Foreground) subset - (introduced in XFA 2.5) - a form in which each page of the XFA form overlays a PDF background. It can be used only for static XFA forms. This architecture uses only a subset of XFA.^[12] It can be packaged inside a regular PDF document or as a standalone XDP file with embedded PDF. In XFAF each XFA field corresponds to a PDF interactive field (AcroForm field).

Packaging

XFA forms can be created and used as PDF 1.5 - 1.7 files or as XDP (XML Data Package). The format of an XFA resource in PDF is described by the XML Data Package Specification.^[13] PDF may contain XFA in XDP format, but XFA may also contain PDF.^[7]

When the XFA (XML Forms Architecture) grammars used for an XFA form are moved from one application to another, they must be packaged as an XML Data Package. The XDP may be a standalone document or it may in turn be carried inside a PDF document.^[12]

XFA Form packaging variants (using XDP):

• as a standalone XML Data Package (XDP) (.xdp file) which can optionally also include a PDF file
• inside a regular PDF Document - used for static forms - XFAF.
• inside a "Shell PDF" - used for the "full XFA" form (dynamic or traditional static) - A Shell PDF file contains only a minimal skeleton of PDF markup plus the complete XFA content, any fonts and images needed for rendering of the form. It minimizes the file size and the rendering overhead is moved from the server to the client.

Packaging an XDP within PDF has the advantage that it is more compact, because PDF is compressed. XDP in PDF can be digitally signed in ways that a standalone XDP cannot.

In contrast, packaging form components within an XML container (XDP) makes it easy for standard XML applications to work with XFA forms. The XML components are human readable and easy editable (in contrast with PDF source code). When in XDP form, an XFA document may be validated using schemas attached to XFA specification.

Compatibility

Most PDF processors do not handle XFA content. When generating a shell PDF it is recommended to include in the PDF markup a simple one-page PDF image displaying a warning message (e.g. "To view the full contents of this document, you need a later version of the PDF viewer.", "The full content of this file cannot be displayed with your current PDF viewer.", "Please wait... If this message is not eventually replaced by the proper contents of the document, your PDF viewer may not be able to display this type of document.", etc.). PDF processors that can render XFA content should either not display the supplied warning page image or replace it quickly with the dynamic form content.

In 2013, as a solution for mobile platforms and desktop platforms without XFA support, Adobe created software that creates online HTML5 fillable forms from XFA (known as Adobe "Mobile Forms"). Mobile Forms are not a single file like a PDF or XDP.^[14][15]

Rich text

Rich text may appear in data supplied to the XFA forms, in XFA templates as default text values, as field captions, or as boilerplate (draw) content.

Starting with PDF 1.5 (XFA 2.02), the text contents of variable text form fields, as well as markup annotations, may include formatting information (style information). These rich text strings are XML documents that conform to the rich text conventions specified for the XML Forms Architecture specification, which is itself a subset of the XHTML 1.0 specification, augmented with a restricted set of CSS2 style attributes.^[13]

In PDF 1.6, PDF supports the rich text elements and attributes specified in the XML Forms Architecture (XFA) Specification, 2.2. In PDF 1.7, PDF supports the rich text elements and attributes specified in the XML Forms Architecture (XFA) Specification, 2.4.^[13] It was announced in 2011 that PDF 2.0 (ISO 32000 Part 2) would reference XFA 3.1,^[16] but when published, PDF 2.0 deprecated it.^[4]

PDF/A

When an XFA form is converted to PDF/A, both the boilerplate and field content are flattened into a PDF appearance stream. PDF/A forbids active content and all XFA content except, optionally, the XML Data Document (forms data created by a user).