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

[nicolaasuni]

Thank you very much, @joebordes, for the careful analysis of the XMP metadata mapping and for the clear before/after comparison using exiftool - it is genuinely appreciated.

TCPDF 6 is now deprecated and no further changes will be merged into this repository. Please see the pinned issue Thank You - and the Future of TCPDF for the full explanation and the path forward.

The distinction between dc:description, dc:subject, and pdf:Keywords in the XMP stream is handled correctly in tc-lib-pdf. If you find any gap there, feel free to open a PR or issue in that repository. If you need any help adapting your fix to the new library, please open a discussion and I will do my best to assist.

I am leaving this PR open in case you or anyone else wishes to continue the discussion, but it is unlikely that this PR will ever be merged.

Thank you again for your patience and understanding.