TweetFollow Us on Twitter

Fill Online PDF Forms Using HTML Forms

Volume Number: 20 (2004)
Issue Number: 11
Column Tag: Programming

Fill Online PDF Forms Using HTML Forms

by Sid Steward

Collect data using an HTML form, To deliver a filled-out PDF form that works in Preview

Adobe's Portable Document Format (PDF) is really only as portable as the viewer used to read or print it. This has become an issue in recent years as the Adobe Reader (nee Acrobat Reader) has evolved to support some platforms better than others. Web publishers who desire maximum portability must now take stock: would this work on OS X or Linux as well as Windows? This issue is complicated by the rise of alternative PDF viewers such as Apple's Preview and alternative web browsers such as Konqueror.

Basic PDF viewing and printing is generally okay. Interactive PDF forms, however, are a different story. Adobe Reader on Windows integrates closely with popular web browsers, allowing a web developer to drive an interactive PDF form filling session using the web server (e.g., OS X users, however, won't have the same experience, nor will many Linux users.

One solution is to use HTML form features instead of PDF form features when collecting data. The web server can manage this data collection session, providing data validation and any necessary database access. When the form is complete, the web server can load the PDF form with the user's data, flatten the form, and then serve it to the user. "Flattening" makes the dynamic form data a permanent part of the page, so the resulting PDF will display properly using any PDF viewer.

Collecting data online using HTML forms is old hat. We'll discuss the part where you pack this data into the PDF form for delivery to your user. We'll also talk about how you can automatically convert a PDF form into an HTML form. My free, command-line tool, pdftk, makes both of these possible. We'll need to discuss how to get pdftk working on OS X (it also works on FreeBSD, Linux, Solaris and Windows). We should also touch on PDF forms.

PDF Forms

Using Adobe Acrobat 4, 5, or Acrobat 6.0 Pro (but not 6.0 Standard), you can add interactive form fields to PDF documents. PDF form fields closely resemble the form fields available to HTML form programmers. You have text boxes, check boxes, radio buttons, combo boxes, list boxes, and buttons. These can be further configured to suit your needs. For example, a text box can be configured to be multi-line or to mask password input, and buttons can be configured to submit the form data to a web server.

You can even program PDF forms using JavaScript, although the PDF document object model is quite different than the DOM familiar to web developers. To learn more about programming PDF using JavaScript, see the Acrobat JavaScript Object Specification ( developer/pdfs/tn/5186AcroJS.pdf) and the Acrobat JavaScript Scripting Guide (http://partners.adobe. com/asn/acrobat/sdk/public/docs/AcroJSGuide.pdf). We won't discuss using JavaScript with PDF forms, here. Though, I will mention the site html, where you will find JavaScript powered PDF games, such as Tic-Tac-Toe and Naval Battle.

For our purposes, the important thing about PDF forms is that you can permanently merge them with form data. You can do this using Acrobat, or you can use the free, command-line PDF Toolkit, pdftk.

Pdftk, the PDF Toolkit

Pdftk is a command-line program for manipulating PDF documents; it is free software. I created it one year ago to fulfill my own requirements. Since then, I have added features that I believed this free, general-purpose PDF tool should provide. It can:

  • Merge PDF Documents
  • Split PDF Pages into a New Document
  • Decrypt Input as Necessary (Password Required)
  • Encrypt Output as Desired
  • Fill PDF Forms with FDF Data and/or Flatten Forms
  • Apply a Background Watermark
  • Report on PDF Metrics such as Metadata, Bookmarks, and Page Labels
  • Update PDF Metadata
  • Attach Files to PDF Pages or the PDF Document
  • Unpack PDF Attachments
  • Burst a PDF Document into Single Pages
  • Uncompress and Re-Compress Page Streams
  • Repair Corrupted PDF (Where Possible)

The pdftk web site ( describes these features and explains how to get pdftk working on your system. Pdftk does not require Acrobat or Java. An OS X 10.3 installer is available for pdftk 1.11 from the site. Alternatively, you can build pdftk yourself, a non-trivial task described below. You must have version 1.11 if you want to automatically create an HTML form from a PDF form.

Under pdftk's hood, the iText PDF library does all the heavy lifting. iText is written in Java, but I prefer programming in C++. So I used GCJ, the Java compiler maintained as part of GNU GCC. GCJ allows me to compile iText and then link it with my C++ program. The result is a stand-alone binary that does not need Java. Very cool.

The problem is that your OS X system probably doesn't have GCJ. You must build GCJ (along with GCC) before you can build pdftk on OS X. Happily, John M. Gabriele provides instructions at: gcj_osx/gcj_on_osx.html. Brian D. Foy documents his experience building GCJ and pdftk at:

After building and installing GCC/GCJ, download and unpack the latest version of pdftk (currently 1.11) from If you configured GCC/GCJ with --prefix=/usr/local/gcj as John describes, then you won't need to edit the OS X Makefile. Otherwise you will need to edit Makefile.MacOSX so that TOOLPATH matches your location of GCC/GCJ.

After unpacking pdftk 1.11, change into the pdftk-1.11/pdftk directory and run make -f Makefile.MacOSX. It will take awhile to finish compiling. When it is done, move the resulting pdftk program to a convenient location in your $PATH, such as /usr/bin. Test pdftk by displaying its help page:

pdftk --help
and merging a couple PDFs together:
pdftk 1.pdf 2.pdf cat output 12.pdf

Note that you cannot name pdftk's output PDF so it overwrites an input PDF. Also, upon success, pdftk will overwrite files with its output without warning. Change this latter behavior by appending do_ask to the end of the command line, or change the ASK_ABOUT_WARNINGS setting in Makefile.MacOSX and recompile pdftk.

Before we begin using pdftk to fill PDF forms with data, let's talk about FDF.

Store Form Data Using FDF

FDF is Adobe's Forms Data Format, a file format for storing and managing PDF form data. FDF is usually plain text, so you can create it pretty easily using a text editor or your favorite scripting language. FDF is fully documented in section 8.6.6 of the PDF Reference, fourth edition. You can download the latest version of the PDF Reference from: pdf/specifications.jsp. Here is an example of an FDF file that assigns the value "San Francisco" to the PDF field named city:

1 0 obj
<< /FDF << /Fields [	<< /T (city)  /V (San Francisco) >>
                                 << /T (state) /V (California) >> ] >>
trailer << /Root 1 0 R >>

To simplify FDF creation, I created a PHP program called forge_fdf. It takes form data as name/value pairs and then spins out the matching FDF. The program logic should be easy to reproduce in any language. Visit to download the latest version. In PHP, you would use forge_fdf like so:

require_once( 'forge_fdf.php' );

// use this array for text fields, combo box, and list box form field values
$fdf_data_strings= array( 'city'  => 'San Francisco',
                          'state' => 'California' );

// use this array for check box and radio button values
$fdf_data_names= array();

// these aren't used in this example
$fields_hidden= array();
$fields_readonly= array();

$fdf= forge_fdf(	'',
                        $fields_readonly );

$fdf_fn= tempnam( '.', 'fdf' );
$fp= fopen( $fdf_fn, 'w' );
if( $fp ) {
   fwrite( $fp, $fdf );
   fclose( $fp );

   // serve PDF, but prompt the user to save it to disk
   header( 'Content-type: application/pdf' );
   header(	'Content-disposition: attachment; '.
                'filename=filled_form.pdf' );

   // our pdftk magic; "flatten" merges data with the page
   passthru(   'pdftk form.pdf fill_form '. $fdf_fn.
                                         ' output - flatten' );
   unlink( $fdf_fn ); // delete temp file
else { // error
   echo 'Error: unable to write temp fdf file: '. $fdf_fn;

One FDF peculiarity is that text field, combo box and list box form field values are represented as PDF "strings," where check box and radio button values are represented as PDF "names." For our purposes, names and strings are the same; they are just encoded a little differently in the FDF. That is why forge_fdf takes two arrays of data: fdf_data_strings and fdf_data_names; pack them appropriately. By default, check boxes and radio buttons use the values "Yes" and "Off" to represent their true and false states, respectively. The form designer can choose an alternative to "Yes," but "Off" always means false.

The arrays fields_hidden and fields_readonly have no role in this discussion, so you can ignore them.

Now things are beginning to come together. We have a PDF form, we have an FDF data file, and we can also see, above, that pdftk can merge these two files into a single, non-interactive PDF. Let's talk about that.

PDF Form Filling and Flattening with Pdftk

The pdftk command for filling a PDF form looks like this:

pdftk <input PDF form> fill_form <input FDF data> output <output PDF file> [flatten]

The PDF input, the FDF input, and the PDF output can be a filename, a hyphen (-), or "PROMPT." Passing a hyphen into pdftk instead of an input filename causes pdftk to look for data on stdin. Similarly, passing a hyphen into pdftk instead of an output filename causes pdftk to return data on stdout. You can see we used this latter technique in the snippet, above. Finally, you can pass "PROMPT" into pdftk if you would like pdftk to ask you for the necessary filename at run time.

If you include the flatten output option, then all form field data is converted into static page elements. All of the interactive form features are removed, so the result is a plain old PDF that any viewer can handle. If you omit the flatten option, then form fields are filled to match your input data, but they also remain interactive. You can flatten a PDF form at any time by running:

pdftk filled_form.pdf output flattened_form.pdf flatten

So, these are the back-end pieces to our workaround for online PDF forms. We can take form data, cast it into FDF, merge it with the PDF form, and then serve it to the user. Now let's look into creating the front-end HTML form. To help us along the way, we'll use pdftk to discover PDF form field information.

PDF Form Field Discovery with Pdftk

A PDF form can have dozens of interactive fields. Manually mirroring these fields in HTML would be cumbersome and error-prone. Instead, let's use one of pdftk's reporting features. You can learn everything you need to know about your PDF's interactive form fields by running:

pdftk form.pdf dump_data_fields > form.pdf.fields

This will create an easily parsible plain text report on your form's fields. The output might look like this:

FieldType: Text
FieldName: name_last
FieldNameAlt: Last Name
FieldFlags: 8392706
FieldJustification: Left
FieldMaxLength: 200
FieldType: Button
FieldName: previous1
FieldFlags: 0
FieldJustification: Left
FieldStateOption: Off
FieldStateOption: Yes
FieldType: Choice
FieldName: select_one
FieldFlags: 4587520
FieldValue: a
FieldValueDefault: c
FieldStateOption: a
FieldStateOption: b
FieldStateOption: c

You can see that the field named title has a maximum length of 200 characters, that a button named previous1 has two possible states: Off and Yes, and a combo box named select_one has three possible states: a, b, and c. Note that push buttons, check boxes and radio buttons all have a FieldType of Button. To tell them apart, you must consult the FieldFlags. Similarly, list boxes and combo boxes both have a FieldType of Choice. See section 8.6 of the PDF Reference for details on field flags and their meanings. We won't be bothering with them, here.

This plain text report should provide you with all the information you need to create an HTML interface to your form. For fun, let's use PHP to do this automatically. Here's a script that reads this text report and generates an HTML form to suit. If you added a "Short Description" to each field in Acrobat, then that text will appear as the FieldNameAlt entry in our report. Our script will use this information, if present, to label the HTML field.


// this function loads a data file created using pdftk dump_data_fields
load_field_data( $field_report_fn )
   $ret_val= array();

   $fp= fopen( $field_report_fn, "r" );
   if( $fp ) {
      $line= '';
      $rec= array();
      while( ($line= fgets($fp, 2048))!== FALSE ) {
         $line= rtrim( $line ); // remove trailing whitespace
         if( $line== '---' ) {
            if( 0< count($rec) ) { // end of record
               $ret_val[]= $rec;
               $rec= array();
            continue; // skip to next line

         // split line into name and value
         $data_pos= strpos( $line, ':' );
         $name= substr( $line, 0, $data_pos+ 1 );
         $value= substr( $line, $data_pos+ 2 );

         if( $name== 'FieldStateOption:' ) {
            // pack state options into their own sub-array
            if( !array_key_exists('FieldStateOption:',$rec) ) {
               $rec['FieldStateOption:']= array();
            $rec['FieldStateOption:'][]= $value;
         else {
            $rec[ $name ]= $value;
      if( 0< count($rec)) { // pack final record
         $ret_val[]= $rec;

      fclose( $fp );

   return $ret_val;
// open our web page; the form action is a script we provide, below
echo '<html>
<form method="POST" action="pdf_form_fill.php">
// create the file form.pdf.fields using pdftk's dump_data_fields
$field_arr= load_field_data( 'form.pdf.fields' );
foreach( $field_arr as $field ) { // iterate form fields
   echo '<tr><td>'; // one row per field
   if(array_key_exists('FieldNameAlt:', $field)) {
      // use human readable name, if available; you can add these in Acrobat
      echo $field['FieldNameAlt:'];
   else {
      echo $field['FieldName:'];
   echo '</td><td>';

   if( $field['FieldType:']== 'Text' ) {
      // construct an HTML text form field to match our PDF text form field;
      // cannot use periods in field names with PHP, so translate them to tildes
      echo   '<input type="text" name="'.
            strtr($field['FieldName:'],'.','~'). '" ';
      // text field default value
      if(array_key_exists('FieldValueDefault:', $field)) {
         echo 'value="'. $field['FieldValueDefault:']. '" ';
      // text field size and maxlength
      if(array_key_exists('FieldMaxLength:', $field)) {
         echo 'maxlength="'. $field['FieldMaxLength:']. '" ';
         if( $field['FieldMaxLength:']< 80 ) {
            echo 'size="'. $field['FieldMaxLength:']. '" ';
         else {
            echo 'size="80" ';
      echo '>';
   else if(array_key_exists('FieldStateOption:', $field)) {
      // use an HTML selection field for all other PDF form fields
      // (check boxes, radio buttons, list boxes, combo boxes);
      // cannot use periods in field names with PHP, so translate them to tildes
      echo   '<select name="'.
            strtr($field['FieldName:'], '.', '~'). '">';
      foreach( $field['FieldStateOption:'] as $option ) {
         echo '<option>'.$option.'</option>';
      echo '</select>';
   echo "</td></tr>\n";
// close our table and our HTML page; don't forget the submit button
echo '</table>
<input type="submit" value="Create PDF">

Now, we need a companion script that takes this submitted data, packs it into the PDF form and serves it to the user. This script is the pdf_form_fill.php action in our above HTML form. It looks much like our earlier form filling example:

require_once( 'forge_fdf.php' );

$fdf_data_strings= array();
$fdf_data_names= array();

// funny thing; for our purpose, we can get away with packing everything
// everything into fdf_data_strings; that's handy
foreach( $_POST as $key => $value ) {
   // translate tildes back to periods
   $fdf_data_strings[ strtr($key, '~', '.') ]= $value;
// ignore these in this example
$fields_hidden= array();
$fields_readonly= array();

$fdf= forge_fdf( '',
                        $fields_readonly );

$fdf_fn= tempnam( '.', 'fdf' );
$fp= fopen( $fdf_fn, 'w' );
if( $fp ) {
   fwrite( $fp, $fdf );
   fclose( $fp );

   header(   'Content-type: application/pdf' );
   header(   'Content-disposition: attachment; '.
             'filename=filled_form.pdf' );

   passthru(   'pdftk form.pdf fill_form '. $fdf_fn.
               ' output - flatten' );
   unlink( $fdf_fn ); // delete temp file
else { // error
   echo 'Error: unable to write temp fdf file: '. $fdf_fn;

When filling forms this way, it turns out you can pass everything into forge_fdf using the fdf_data_strings array; there's no need to use fdf_data_names. That's handy.

Now the Fun Begins

We have done it! We have created an HTML front-end to filling PDF forms. This is where the fun begins. You can now take everything you know about web programming, such as data validation and database access, and use it to fill PDF forms. Your users will be glad, too, because your resulting PDFs will work in alternative viewers such as Preview, and because you give them a filled-out PDF form for their records (which Adobe Reader does not provide).

To see an online example of these scripts, visit You will also find the code, quoted in this article, available for download.

Sid Steward is a longtime PDF service provider and software developer. He developed the free PDF Toolkit ( and wrote the book PDF Hacks (O'Reilly Media). You can reach him at


Community Search:
MacTech Search:

Software Updates via MacUpdate

GarageSale 6.9.2 - Create outstanding eB...
GarageSale is a slick, full-featured client application for the eBay online auction system. Create and manage your auctions with ease. With GarageSale, you can create, edit, track, and manage... Read more
calibre 2.17 - Complete e-library manage...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
OmniGraffle Pro 6.1.2 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniGraffle 6.1.2 - Create diagrams, flo...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more
RoboForm 2.0.2 - Password manager; syncs...
RoboForm is a password manager that offers one-click login, mobile syncing, easy form filling, and reliable security. Password Manager. RoboForm remembers your passwords so you don't have to! Just... Read more
Apple MainStage 3.1 - Live performance t...
Love the sound you got on your recording? MainStage 3 makes it easy to bring all the same instruments and effects to the stage. Everything from the Sound Library and Smart Controls you're familiar... Read more
Freeway Pro 7.0.2 - Drag-and-drop Web de...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With its user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
A Better Finder Rename 9.44 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
Stacks 2.6.9 - New way to create pages i...
Stacks is a new way to create pages in RapidWeaver. It's a plugin designed to combine drag-and-drop simplicity with the power of fluid layout. Features: Fluid Layout: Stacks lets you build pages... Read more
Sid Meier's Civilization: Beyond Ea...
Sid Meier's Civilization: Beyond Earth is a new science-fiction-themed entry into the award-winning Civilization series. Set in the future, global events have destabilized the world leading to a... Read more

Mediocre, the Team Behind Smash Hit, is...
Mediocre, the Team Behind Smash Hit, is Teasing Their Latest Unnamed Project Posted by Jessica Fisher on January 26th, 2015 [ permalink ] | Read more »
Heroes of Gaia Review
Heroes of Gaia Review By Campbell Bird on January 26th, 2015 Our Rating: :: TIMERS OF MIGHT AND MAGICUniversal App - Designed for iPhone and iPad This free-to-play rpg looks a lot like Heroes of Might and Magic, but it’s poor... | Read more »
Choice Provisions is Set to Launch Destr...
Choice Provisions is Set to Launch Destructamundo on iOS This Month Posted by Tre Lawrence on January 23rd, 2015 [ permalink ] Choice Provisions – home stable to | Read more »
King of Thieves – An Interview With Zept...
Ahead of the release of ZeptoLab’s King of Thieves, we were able to ask ZeptoLab’s co-founder, Semyon Voinov, a few questions about the inspiration behind the game and what that means for the Cut the Rope franchise. | Read more »
Handle Review
Handle Review By Jennifer Allen on January 23rd, 2015 Our Rating: :: SPEEDY ORGANIZINGUniversal App - Designed for iPhone and iPad Handle is a very convenient way of juggling your emails, To Do list, and Calendar all through one... | Read more »
The New Disney Inquizitive App Offers a...
The New Disney Inquizitive App Offers a Place for Fans to Take Disney Quizzes Posted by Tre Lawrence on January 23rd, 2015 [ permalink ] | Read more »
Hands-On With Cut the Rope Developer Zep...
Marking quite a departure from ZeptoLab’s past successes, namely the Cut The Rope series, King of Thieves is shaping up to be quite promising. Due for release in February, we were lucky enough to have some time with a preview build to see exactly... | Read more »
Fast Fishing Review
Fast Fishing Review By Jennifer Allen on January 23rd, 2015 Our Rating: :: LIVES UP TO ITS NAMEUniversal App - Designed for iPhone and iPad Fishing is far from relaxing in Fast Fishing, but it is fun.   | Read more »
Head Back to Dark World of Arnashia in B...
Head Back to Dark World of Arnashia in Blood Brothers 2 Posted by Jessica Fisher on January 23rd, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Saved Review
Saved Review By Jennifer Allen on January 23rd, 2015 Our Rating: :: SIMPLE BUDGETINGiPhone App - Designed for the iPhone, compatible with the iPad Saved is a convenient and speedy way of adding expenses and keeping track of your... | Read more »

Price Scanner via

Stir Kinetic Desk M1 Standing Or Sitting Desk...
The age of the standing desk is upon us, and according to medical research, it’s arriving none too soon. The World Health Organization (WHO), reports that 60 to 85 percent of people worldwide lead... Read more
Bosch Opens North American eBike Conversion H...
Following its entry into the U.S. eBike market in early 2014, Bosch has established a new headquarters office for Bosch eBike Systems ( in Southern California, expanding the... Read more
13-inch 2.4GHz Retina MacBook Pro (Apple refu...
The Apple Store has previous-generation Apple Certified Refurbished 13″ 2.4GHz/128GB Retina MacBook Pros available for $999. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.4GHz/... Read more
13-inch 2.6GHz Retina MacBook Pro on sale for...
Adorama has the 13″ 2.6GHz/128GB Retina MacBook Pro on sale for $1189.99, $110 off MSRP. Shipping is free, and Adorama charges NY & NJ sales tax only. Read more
College Student Deals are back, additional $5...
Take an additional $50 off all MacBooks and iMacs at Best Buy Online with their College Students Deals Savings, valid through April 11, 2015. Anyone with a valid .EDU email address can take advantage... Read more
iPhone 6 and 6 Plus GIve Apple Half Of US Mob...
Chicago-based Consumer Intelligence Research Partners, LLC (CIRP) have released analysis of the results of its research on mobile phone manufacturers for the calendar quarter that ended December 31,... Read more
Save $100 on MacBook Airs with 256GB of stora...
B&H Photo has 256GB MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.4GHz/256GB MacBook Air: $999 $100 off MSRP - 13″ 1.4GHz/256GB MacBook... Read more
21-inch 2.7GHz iMac on sale for $1179, save $...
B&H Photo has the 21″ 2.7GHz iMac on sale for $1179 including free shipping plus NY sales tax only. Their price is $120 off MSRP, and it’s the lowest price available for this model from any... Read more
iPhone Usage Rates by State Correlate With Ed...
Chitika Insights notes that despite iPhones being the largest source of smartphone Internet traffic in North America, their latest study finds a relatively high degree of variation of iPhone usage... Read more
ProGearX Extendable Pole “Pov/Selfie Stick” M...
There’s something inescapably narcissistic about the concept of selfies as they’ve developed as a smartphone-driven social (particularly social media) phenomenon that rubs me the wrong way. However,... Read more

Jobs Board

*Apple* Acura/Subaru Service Technicians - A...
Apple Automotive is one of the fastest growing dealer…and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive , Read more
Business Development Manager - *Apple* Pay...
**Job Summary** Apple Pay is seeking an experienced business development manager to support the identification, recruitment, negotiation and ongoing management of Read more
*Apple* Solutions Consultant (ASC)- Retail S...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
*Apple* Lead Operator, GSOC - Apple (United...
**Job Summary** Apple is seeking an exceptional, customer service oriented and experienced persons to fulfill the role of Apple Lead Operator (ALO) as part of the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.