With the file extension XFDF, form data of PDF documents are stored in an XML-based format (XML Forms Data Format). In addition to the normal documents with text and images, the PDF format also offers the possibility of creating PDF documents with input fields, for example text fields or drop-down lists.
If you fill out such a pdf file, you can usually only print it out with the Acrobat Reader, because the Adobe Acrobat Reader can load form data, which exists as an XFDF file, but can not normally save it.
However, the creator of a form may be able to send the form data to a form server, for example, with an FDF Toolkit application or store it locally. In this way you do not need to transfer the entire pdf file, just the actual data. This is mainly used in automated form data processing.
Other pdf display programs, for example pdf-XChange, offer the possibility to directly save or load XFDF files and thus to fill in a form or to save the data locally. Adobe Acrobat XML form data
Most often resolving problems with opening XFDF files is very simple. Just install an appropriate program that supports such files. All of the listed programs support XFDF files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of XFDF files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate XFDF files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Adobe Reader applications is not on the list, select "Browse" option in order to manually locate the directory where Adobe Reader has been installed.
Sometimes problems with opening XFDF files may not lie with the application itself, but can arise due to other causes, such as: