The file extension FDF saves form data of PDF documents. 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 or drop-down lists.
If you fill out such a pdf file, you can only print it out with the Acrobat Reader, because the Acrobat Reader can load form data, which exists as a FDF file, but can not normally save it.
However, the creator of a form may provide the option to submit the form data to a form server, for example, with an FDF Toolkit application, or have it stored 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 FDF files and thus to fill in a form or to save the data locally.
Most often resolving problems with opening FDF files is very simple. Just install an appropriate program that supports such files. All of the listed programs support FDF files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of FDF 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 FDF 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 Acrobat applications is not on the list, select "Browse" option in order to manually locate the directory where Adobe Acrobat has been installed.
Sometimes problems with opening FDF files may not lie with the application itself, but can arise due to other causes, such as: