Hack 78 Permanently Merge a PDF Form and its Data
Provide online users with a copy of their completed form to save.
Adobe Reader enables a user to add, change, view, and print form data, but it does not enable a user to save the filled-in PDF form to disk. Saving the file produces a lovely copy of an empty form. How annoying!
Correct this problem server-side by merging the PDF form and its data. Then, offer this filled-in form as a download for the user's records. After merging, the form fields remain interactive, even though they display the user's data. Go a step further and flatten this form so that field data becomes a permanent part of the PDF pages. After flattening, filled-in fields are no longer interactive. You can merge and flatten forms using the iText library or our command-line pdftk. Both are free software.
6.6.1 Merge or Flatten a Form and Its Data in Java
The iText library (http://www.lowagie.com/iText/ or http://itextpdf.sf.net) is a remarkable tool for manipulating PDF documents. The following Java program, merge_pdf_fdf, demonstrates how to merge or flatten a PDF and its form data FDF [Hack #77] using iText. Run this code from your command line, or integrate it into your web application.
/*
merge_pdf_fdf, version 1.0
merge an input PDF file with an input FDF file
to create a filled-in PDF; optionally flatten the
FDF data so that it becomes part of the page
http://www.pdfhacks.com/merge_pdf_fdf/
invoke from the command line like this:
java -classpath ./itext-paulo.jar:. \
merge_pdf_fdf input.pdf input.fdf output.pdf
or:
java -classpath ./itext-paulo.jar:. \
merge_pdf_fdf input.pdf input.fdf output.pdf flatten
adjust the classpath to the location of your iText jar
*/
import java.io.*;
import com.lowagie.text.pdf.*;
public class merge_pdf_fdf extends java.lang.Object {
public static void main(String args[]) {
if ( args.length == 3 || args.length == 4 ) {
try {
// the input PDF
PdfReader reader =
new PdfReader( args[0] );
reader.consolidateNamedDestinations( );
reader.removeUnusedObjects( );
// the input FDF
FdfReader fdf_reader=
new FdfReader( args[1] );
// PdfStamper acts like a PdfWriter
PdfStamper pdf_stamper=
new PdfStamper( reader,
new FileOutputStream( args[2] ) );
if( args.length == 4 ) { // "flatten"
// filled-in data becomes a permanent part of the page
pdf_stamper.setFormFlattening( true );
}
else {
// filled-in data will 'stick' to the form fields,
// but it will remain interactive
pdf_stamper.setFormFlattening( false );
}
// sets the form fields from the input FDF
AcroFields fields=
pdf_stamper.getAcroFields( );
fields.setFields( fdf_reader );
// closing the stamper closes the underlying
// PdfWriter; the PDF document is written
pdf_stamper.close( );
}
catch( Exception ee ) {
ee.printStackTrace( );
}
}
else { // input error
System.err.println("arguments: file1.pdf file2.fdf destfile [flatten]");
}
}
}To create a command-line Java program, copy the preceding code into a file named merge_pdf_fdf.java. Then, compile merge_pdf_fdf.java using javac, setting the classpath to the name and location of your iText jar:
javac -classpath ./itext-paulo.jar merge_pdf_fdf.javaFinally, invoke merge_pdf_fdf like so:
java -classpath ./itext-paulo.jar :. \ merge_pdf_fdf input.pdf input.fdf output.pdf
6.6.2 Merge or Flatten a Form and Its Data with pdftk
Use pdftk [Hack #79] to merge a form with an FDF datafile [Hack #77] and create a new PDF. The fields will display the given data, but they also remain interactive. pdftk's fill_form operation takes the filename of an FDF file as its argument. For example:
pdftk form.pdf fill_form data.fdf output filled_form.pdf
You can't combine the fill_form operation with any other operation (e.g., cat), but you can supply additional output options for encryption [Hack #52] .
Flatten form data permanently into the page by adding the flatten_form output option. The resulting PDF data will no longer be interactive.
pdftk form.pdf fill_form data.fdf output filled_form.pdf flatten_form
Or, if your PDF form already has field data, just flatten it:
pdftk filled_form.pdf output flattened_form.pdf flatten_form
6.6.3 Merge or Flatten with pdftk in PHP
After installing pdftk on your web server, you can invoke it from your PHP scripts to merge PDF forms with FDF data. Use our PHP script forge_fdf [Hack #77] to cast your data into FDF. Then, save this FDF data into a temporary file. Finally, call pdftk to create a new PDF from your PDF form and FDF data.
The following PHP code could be used for this purpose:
<?php
// session_fdf is your function for converting
// the user's session state into an FDF string
$fdf_ss= session_fdf( $_GET['id'] );
$temp_fn= tempnam( '/tmp', 'tempfdf' );
$temp_fp= fopen( $temp_fn, 'wb' );
if( $temp_fp ) {
fwrite( $temp_fp, $fdf_ss );
fclose( $temp_fp );
header( 'Content-type: application/pdf' );
passthru( '/usr/local/bin/pdftk form.pdf fill_form '.$temp_fn.
' output - flatten' ); // output to stdout (-)
unlink( $temp_fn );
}
?>
