Working With FDFs: Forms Data Files

If you are a designer, you’ll rarely come across an FDF file. In fact, you may have never even heard of FDF, since it’s not among the familiar formats that designers know and love. But there’s a lot to like about FDFs: their compact nature can simplify your workflow and in some instances, save you a lot of time and effort.

What is FDF?

FDF stands for “Forms Data Format.” Despite its name, an FDF file can contain more than forms data. It can also contain comments for a PDF file.

I started using FDF files a few years ago. I write very long owner’s manuals, and I needed an easy way for my clients to provide digital comments on the PDF proofs that I would send them. Specifically, I needed my clients to:

  1. Add their comments to the PDF proof using PDF commenting tools
  2. Send the comments back to me without faxing, scanning, or trying to email the entire 50 MB file
  3. Be able to use one of their existing familiar tools to transfer the comments back to me (and not have to install and configure an FTP client)

With a little research, I settled on FDF files. With an FDF workflow, the client can mark up the PDF using PDF commenting tools, and then export the FDF file and email it back to me. FDF files are very small, and so will never get stuck in an email system due to file size limitations.

Note the file size: only 30k!

Why have we never heard of FDF before?

To be honest, FDF files aren’t very glamorous. They have no user interface, and when viewed independently, they are useless to graphic designers. I imagine that Adobe would probably rather show off the flashier, UI-rich ways of sharing comments: like and Shared Reviews (which I personally find to be rather unstable). But sharing FDF files over email is practically bulletproof. It’s stable. And it’s easy. But it’s not sexy. It just works.

An FDF file is a handy way of having stand-alone PDF comments. If you try to open an FDF file separate from its original PDF file, it won’t make much sense. It’s just a bunch of code and coordinates, with a little bit of English mixed in.

FDF viewed in TextWrangler: this text is the content of a yellow sticky note.

But if you import the FDF file into its accompanying PDF file, the information contained within the PDF can be viewed in context and makes a whole lot more sense. Think of it this way: the parent PDF is the lens through which we can clearly see an FDF file in the proper context.

The same yellow sticky note viewed in Acrobat


How to export an FDF file

To export PDF comments to FDF in Adobe Acrobat: go to the Comments Pane and select Comments List > Options > Export all to Data File…

This will export all your comments to a data file. Then you can email those comments back to whoever sent you the PDF. Keep in mind that each FDF knows which PDF document it is supposed to go with. The parent PDF files are not interchangeable. So if you try to import an FDF file into a PDF with the wrong file name, you’ll get an error message like this:

Another reason FDF files are great: Comment Recovery

So besides some of the other reasons I love FDF files: small file size, easy import and export, and the ability to contains tons of data in a text file, there is one more reason I love FDF files: data recovery.

Let’s say you’re commenting on a PDF over a network connection. You’re happily working away, marking up your PDF with sticky notes, arrows, and text edits. But think now: when was the last time you saved the file? What happens if you lose your network connection?

If you’re an InDesign user, like me, you may take for granted InDesign’s magical document recovery feature. In the background, InDesign automatically saves the changes you make to your file. So if the application crashes, it’s not a huge deal, because generally you can recover your work. But this is not so with Acrobat! Acrobat sometimes is able to recover documents, but I find it spotty at best.

So back to today’s scenario: you’re working happily in Acrobat, but then for any number of reasons, you lose your connection to the file (someone restarts the wireless router, the server gets rebooted, etc). What happens to that PDF that you’ve spent hours commenting on? Chances are good that even when you reconnect to the server, the PDF will refuse to save. So, you have a couple of choices:

  1. Close the PDF and lose all your work. Shout in frustration.
  2. Save your PDF comments out separately, then take a deep breath, close the PDF and reopen it, then reimport the comments. Heave a sigh of relief and give yourself a pat on the back for knowing how to use those plain but powerful FDF files.


Posted on: February 17, 2014

Kelly Vaughn

Design education: ongoing at the University of Hard Knocks. I am graphic designer, technical writer, illustrator, and knitter. I own my own marine publishing company specializing in owner's manuals for custom yachts. I love to blog about InDesign, Acrobat, and obscure ways to use software to make work easier and more productive at DocumentGeek and

6 Comments on Working With FDFs: Forms Data Files

  1. Good overview over what FDF can do with your comments.

    And that’s only one part of what can be done with FDF…

    It is indeed a rather unknown territory…

  2. I didn’t know about FDFs…but I can see exactly where they’re useful. Thanks Kelly for the concise, clear introduction to them.

  3. Aaron Zalonis

    April 8, 2014 at 1:57 am


    This is so much better than having to attempt to reduce the file size of a pdf when you’re dealing with a catalog composed of really large images (like for an art museum.) Even a reduced-size pdf isn’t a big help. I’ll have to send a link to this article along the next time I send someone an .FDF file, so they know what to do with them.

    Thanks for shining light on the elusive .FDF.

  4. I found another great use for FDFs: globally changing the font size of PDF sticky note text. Read it here:

  5. Robert Willey

    May 14, 2018 at 7:06 pm

    God bless you! I was about to start screaming over a ton of lost work and take it out on the poor, innocent dog. Your column worked!

  6. Wow thanks Kelly! I had lost all the text in a pdf and all that was left was the comments – despair!! I almost cried with happiness when this fix worked! God bless you indeed!!

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