Filling out PDF Forms with PDFtk and PHP

This article explains how to use PHP and PDFtk Server (referred to as PDFtk) to populate PDF forms. It's a common need when handling document workflows, especially for client documents needing processing by third parties or when submitting CVs. PDFs handle various data types, making them ideal for this purpose.

Key Concepts:

• PDFtk is a powerful command-line tool for PDF manipulation, including form filling.
• Installation on Linux is straightforward (sudo apt-get install pdftk), verifiable with pdftk --version.
• FDF (Form Data File) is a simple text format for storing form data, easily integrated with PDFtk.
• The PHP script generates an FDF file from user input, uses PDFtk's fill_form to populate the PDF, and optionally flattens the result for immutability.
• A PHP wrapper class simplifies the process, offering methods for saving and downloading the completed form.

Installation and Verification:

Using Homestead Improved (or a similar environment), install PDFtk via SSH:

sudo apt-get install pdftk
pdftk --version

The version output confirms successful installation.

How it Works: FDF Files

PDFtk uses FDF files to interact with PDF forms. An FDF file is a plain-text file with a simple structure:

• Header: %FDF-1.2\n1 0 obj (standard for all FDF files)
• Content: Contains form data entries, each line representing a field. The format is /T(FieldName) /V(FieldValue)
• Footer: ] >> >>\nendobj\ntrailer\n>\n%%EOF (standard for all FDF files)

To determine field names, use Adobe Acrobat Pro or PDFtk's dump_data_fields:

pdftk path/to/the/form.pdf dump_data_fields > field_names.txt

PHP Script and PDFtk Interaction:

A sample PDF form (shown below) will be used to illustrate the process.

This PHP script populates the form:

<?php
$fname = 'John';
$lname = 'Smith';
$occupation = 'Teacher';
$age = '45';
$gender = 'male';

$fdf_header = '%FDF-1.2\n1 0 obj\n<</FDF ';
$fdf_footer = '] >> >>\nendobj\ntrailer\n>\n%%EOF';
$fdf_content = "/T(first_name) /V({$fname})\n/T(last_name) /V({$lname})\n/T(occupation) /V({$occupation})\n/T(age) /V({$age})\n/T(gender) /V({$gender})\n";

$content = $fdf_header . $fdf_content . $fdf_footer;
$FDFfile = tempnam(sys_get_temp_dir(), gethostname());
file_put_contents($FDFfile, $content);

exec("pdftk form.pdf fill_form {$FDFfile} output output.pdf");
unlink($FDFfile);
?>

This script creates a temporary FDF file, uses exec() to run the PDFtk command, and then deletes the temporary file. The output.pdf file will contain the filled form.

Flattening and Downloading:

To prevent further edits, add flatten to the pdftk command. To download directly, add headers to the PHP script:

// ... previous code ...
exec("pdftk form.pdf fill_form {$FDFfile} output output.pdf flatten");
// ... download headers and readfile('output.pdf') ...

PDFtk Wrapper Class:

A more reusable approach involves creating a PHP class (PdfForm.php) to encapsulate the PDFtk interaction. This class would handle temporary file management, FDF creation, form filling, flattening, saving, and downloading. The usage would be significantly cleaner:

<?php
require 'PdfForm.php';
$data = ['first_name' => 'John', 'last_name' => 'Smith', /* ... other fields */];
$pdf = new PdfForm('form.pdf', $data);
$pdf->flatten()->save('output.pdf')->download();
?>

This improved structure promotes code reusability and maintainability. The full class implementation details are omitted for brevity but are available in the original article's GitHub repository (as mentioned in the original text). The class would include methods for extracting field information (fields()), creating the FDF file (makeFdf()), and handling the PDFtk interaction.

Frequently Asked Questions (FAQs): The original article includes a comprehensive FAQ section addressing common issues and advanced usage scenarios, such as handling errors, filling multiple forms, and securing the output PDF. This information is omitted here for brevity but is available in the original text.

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