Fix/xmp description subject

[joebordes]

PR for issue #817

joe:~/TCPDF$ php examples/example_001.php  > example001.pdf
joe:~/TCPDF$ exiftool -XMP:All example001.pdf 
XMP Toolkit                     : Adobe XMP Core 4.2.1-c043 52.372728, 2009/01/18-15:08:04
Format                          : application/pdf
Title                           : TCPDF Example 001
Creator                         : Nicola Asuni
Description                     : TCPDF Tutorial
Subject                         : TCPDF, PDF, example, test, guide
Create Date                     : 2025:10:01 18:35:53+00:00
Creator Tool                    : TCPDF
Modify Date                     : 2025:10:01 18:35:53+00:00
Metadata Date                   : 2025:10:01 18:35:53+00:00
Producer                        : TCPDF 6.10.0 (http://www.tcpdf.org)
Document ID                     : uuid:0cba4c67-099e-fe74-fea7-a279fb39678d
Instance ID                     : uuid:0cba4c67-099e-fe74-fea7-a279fb39678d
Schemas Namespace URI           : http://ns.adobe.com/pdf/1.3/
Schemas Prefix                  : pdf
Schemas Schema                  : Adobe PDF Schema
Schemas Property Category       : internal
Schemas Property Description    : Adobe PDF Schema
Schemas Property Name           : InstanceID
Schemas Property Value Type     : URI

The code that generates that is

$pdf->setCreator(PDF_CREATOR);
$pdf->setAuthor('Nicola Asuni');
$pdf->setTitle('TCPDF Example 001');
$pdf->setSubject('TCPDF Tutorial');
$pdf->setKeywords('TCPDF, PDF, example, test, guide');

We can see here that

• Description contains the Subject
• Subject contains the keywords

With this PR the code to create the PDF is now

$pdf->setCreator(PDF_CREATOR);
$pdf->setAuthor('Nicola Asuni');
$pdf->setTitle('TCPDF Example 001');
$pdf->setSubject('TCPDF Tutorial');
$pdf->setDescription('TCPDF Tutorial Description');
$pdf->setKeywords('TCPDF, PDF, example, test, guide');

and the output is

joe:~/TCPDF$ php examples/example_001.php  > example001.pdf
joe:~/TCPDF$ exiftool -XMP:All example001.pdf 
XMP Toolkit                     : Adobe XMP Core 4.2.1-c043 52.372728, 2009/01/18-15:08:04
Format                          : application/pdf
Title                           : TCPDF Example 001
Creator                         : Nicola Asuni
Description                     : TCPDF Tutorial Description
Subject                         : TCPDF Tutorial
Create Date                     : 2025:10:01 18:54:34+00:00
Creator Tool                    : TCPDF
Modify Date                     : 2025:10:01 18:54:34+00:00
Metadata Date                   : 2025:10:01 18:54:34+00:00
Producer                        : TCPDF 6.10.0 (http://www.tcpdf.org)
Document ID                     : uuid:91da612c-5ad4-9b90-89fb-aa6525362f2f
Instance ID                     : uuid:91da612c-5ad4-9b90-89fb-aa6525362f2f
Schemas Namespace URI           : http://ns.adobe.com/pdf/1.3/
Schemas Prefix                  : pdf
Schemas Schema                  : Adobe PDF Schema
Schemas Property Category       : internal
Schemas Property Description    : Adobe PDF Schema
Schemas Property Name           : InstanceID
Schemas Property Value Type     : URI

where you can see that we have description and subject as per the methods.

[CLAassistant]

All committers have signed the CLA.

[joebordes]

please add the hacktoberfest tag

[williamdes]

Would this not break some users workflow?

[joebordes]

could be, but putting "keywords" in a "subject" field seems wrong to me

@nicolaasuni comments?

[nicolaasuni]

thanks for the explanation, I will review this.

[nicolaasuni]

My understanding is that in a PDF file's metadata, the "subject" field and the Dublin Core (dc) element "dc:description" are distinct but related properties that describe the document's content.

• The "subject" property is part of the legacy "Document Information Dictionary" in a PDF file.
• The "dc:description" element is part of the Extensible Metadata Platform (XMP) metadata stream, which is the modern, standardized way to store metadata in Adobe products and PDF/A compliant files.

While distinct in name and original location, these fields are often synchronized. Indeed in TCPDF the "dc:description" value is set to the "subject" field value.

[nicolaasuni]

In similar ways, "dc:subject" and "keywords" both serve to categorise a PDF document using specific topics or terms. They are essentially two different references for the same information within a modern PDF file.

[nicolaasuni]

not sure about this change. Why keywords was removed?

[joebordes]

Keywords haven't been removed. They are still where they should be; a few more lines after this one, you will find.

$xmp .= "\t\t\t".'<pdf:Keywords>'.TCPDF_STATIC::_escapeXML($this->keywords).'</pdf:Keywords>'."\n";

What I am doing is using subject inside the <dc:subject> section instead of keywords