问题
I want to fill out a dual AcroForm/XFA PDF form automatically. I included an XFA dataset packet and all values showed up in Adobe Reader. I set the V= key in AcroForms entries to the new value and all values showed up alternative PDF readers.
However, when I open the PDF with XFA and AcroForm V= entries in Adobe Reader, only the value of the text field that is currently selected is visible:
I cannot find any mention in the PDF specification of a special flag to set when AcroForms and XFA are present. I hypothesized that the order of the XFA and Field keys may be important, but that's not it either.
How can I change my PDF file so that the values are visible in Adobe Reader on startup, and in PDF readers which only support AcroForms and not XFA?
回答1:
There are 2 questions to be answered:
- Why is Adobe Reader only displaying the field value when the field is selected?
- How to determine if the AcroForm or the XFA is used?
1. Displayed field values
In some cases Adobe Reader/Acrobat will display a form field differently depending on whether it's selected or not. This is typical for a field that has a defined appearance that is different from how Reader/Acrobat would render the field based on its value (and possibly some appearance settings).
When the field is not selected, the defined appearance will be shown. When the field is selected, a preview of how Reader/Acrobat would render it is shown.
Some background:
A form field consists of a logical part (field name, field value, ...), called the field dictionary, and a visualization part, called the widget annotation. The widget annotation can optionally contain an AP entry, containing the appearance streams that define its visualization. Cf. PDF Specification, 1.7, Table 8.15:
AP - dictionary - An appearance dictionary specifying how the annotation is presented visually on the page.
In the sample PDF there are no AP entries, i.e. blank visualizations. This is what's displayed for all the fields. When selecting a field, you see Reader/Acrobat's preview, based on the field value.
You can verify this by changing a field value manually with Reader/Acrobat. In that case, a new appearance will be generated and saved. That field will now be displayed in the same way, regardless of it being selected or not.
Two options to prevent these "blank" fields in Reader/Acrobat:
Generate appearance streams for all form fields. I have done this for one field (by simply re-setting its value using iText, which automatically generates an appearance stream).
The result:
Internal PDF structure:
Set the NeedAppearances entry in the AcroForm dictionary to
true. Cf. PDF Specification, 1.7, Table 8.67:NeedAppearances - boolean - A flag specifying whether to construct appearance streams and appearance dictionaries for all widget annotations in the document
This will trigger the viewer to generate all the appearances:
2. AcroForm or XFA?
In general, a XFA capable viewer will display the XFA form. A viewer without XFA support will use the AcroForm. You can verify this by setting different values for corresponding AcroForm and XFA fields. This is the result, Chrome's built-in PDF viewer on the left (no XFA support), Acrobat on the right:
Knowing that Reader/Acrobat is using the XFA form, why did we still see the blank fields (cf question 1)?
It seems that, when the values of an XFA field and its corresponding AcroForm field are the same, Reader/Acrobat also uses some information from the AcroForm, a.o. its appearance information. When the XFA value is different from the AcroForm value, the AcroForm field seems to be ignored completely.
TL;DR Set NeedAppearances to true to solve blank fields. XFA-incapable viewers will fall back to AcroForm automatically.
(My tests are based on Adobe Acrobat X.)
来源：https://stackoverflow.com/questions/33899913/xfa-values-initially-invisible-when-acroform-values-are-set