ANSWER: FDF stands for "Forms Data Format." FDF is a file format for representing form data and annotations that are contained in a PDF form.

The FDF format was invented by Adobe Systems Incorporated, and it is based on the PDF format. You can find a detailed specification for the FDF format in Adobe's PDF Reference.

The FDF format can be used in a variety of workflows. Here are a couple examples:

Sending form data to a server and receiving modified form data back from the server.

This workflow would look something like this:

  • Form data is submitted to the server in FDF format. (Typically, this would happen when a human user at a client machine clicks a "Submit" button on the form.)

  • On the server, the FDF data is modified.

  • The server sends the modified FDF data back to the client.

  • At the client machine, the fields in the form are populated with the modified data.

Archiving form data. 

This workflow would look something like this:

  • A human user uses Adobe Acrobat or another PDF-editing/viewing application to export the form data in FDF format.

  • The FDF file is saved in the company's archives.

  • To look at the form data, a human user would use Adobe Acrobat or some other PDF-viewing/editing application* to open the FDF file; this would cause the PDF-viewing/editing application to 1) find the PDF form from which the form data was exported, 2) load the form data into the form, 3) display the form with the loaded data on the screen.

You might be wondering why you'd want to archive an FDF file containing the data for a PDF form instead of simply archiving a uniquely named version of the entire PDF form with the data included in it. There are two reasons:

  1. An FDF file containing form data for a PDF form is much smaller than the file containing the PDF form itself, so archiving FDF files requires less storage space than archiving PDF forms.

  2. Some software that people use to view and interact with PDF forms does not allow the user to save a filled-in PDF form.

IMPORTANT NOTE TO DEVELOPERS: An FDF file contains the filename and location of the PDF form from which the form data in that particular FDF file was exported. Adobe Acrobat (and any PDF-viewing/editing application that supports PDF forms) relies on that filename and location in order to retrieve and open the appropriate PDF form when opening an FDF file. In other words: when opening an FDF file, a PDF viewing/editing application assumes that the PDF form from which the form data was exported is available at the specified location.

Therefore, if you are a developer considering implementation of a system that archives FDF data, you'll want to make sure your system has a reliable method of storing the required PDF forms in known locations. Otherwise, it will not always be possible for PDF-viewing/editing applications to retrieve and open the PDF Forms when they are needed.

*Some PDF-viewing/editing applications do not support all features and functionality related to PDF forms.

Creating your own FDF files

As mentioned, the two workflows described above are just examples of how you can utilize FDF data. Both of those workflows rely on a PDF-viewing/editing application such as Adobe Acrobat for creation of the FDF data.

However, you don't have to rely on a PDF-viewing/editing application to generate FDF data — it is possible to generate FDF data yourself, and depending upon what you need to accomplish, it might make sense to do just that. For example, if you have data stored in a database, it would be possible (if you are a programmer or if you have access to someone with programming skills) to extract data from your database and put it in FDF format. Or, if you have a Web site where site visitors enter data into an HTML form, you or your programmer could write a script to convert the data entered by users to FDF format. As stated below, the FDF format is described in detail in the Adobe PDF Reference, so you'd need to read the relevant sections of that document to gain an understanding of the FDF format before you'd be able to generate your own FDF data.

Populating PDF forms with FDF data dynamically

A programmer can use a programmer's library or toolkit to put FDF data into your PDF forms automatically. An Internet search will lead you to companies that offer such libraries/toolkits.

How to get more information about the FDF format

The FDF specification is part of Adobe's PDF specification, so you'll find the FDF specification in Adobe's PDF Reference.

See also What is PDF?
See also What is XFDF?