PDF Metadata

PDF has two different types of metadata: XMP metadata, and DocumentInfo, which is deprecated but still relevant. For backward compatibility, both should contain the same content. pikepdf provides a convenient interface that coordinates edits to both, but is limited to the most common metadata features.

XMP (Extensible Metadata Platform) Metadata is a metadata specification in XML format that is used many formats other than PDF. For full information on XMP, see Adobe’s XMP Developer Center. The XMP Specification also provides useful information.

pikepdf can read compound metadata quantities, but can only modify scalars. For more complex changes consider using the python-xmp-toolkit library and its libexempi dependency; but note that it is not capable of synchronizing changes to the older DocumentInfo metadata.

Automatic metadata updates

By default pikepdf will create a XMP metadata block and set pdf:PDFVersion to a value that matches the PDF version declared elsewhere in the PDF, whenever a PDF is saved. To suppress this behavior, save with pdf.save(..., fix_metadata_version=False).

Also by default, Pdf.open_metadata() will synchronize the XMP metadata with the older document information dictionary. This behavior can also be adjusted using keyword arguments.

Accessing metadata

The XMP metadata stream is attached the PDF’s root object, but to simplify management of this, use pikepdf.Pdf.open_metadata(). The returned pikepdf.models.PdfMetadata object may be used for reading, or entered with a with block to modify and commit changes. If you use this interface, pikepdf will synchronize changes to new and old metadata.

A PDF must still be saved after metadata is changed.

In [1]: pdf = pikepdf.open('../tests/resources/sandwich.pdf')

In [2]: meta = pdf.open_metadata()

In [3]: meta['xmp:CreatorTool']
Out[3]: 'ocrmypdf 5.3.3 / Tesseract OCR-PDF 3.05.01'

If no XMP metadata exists, an empty XMP metadata container will be created.

Open metadata in a with block to open it for editing. When the block is exited, changes are committed (updating XMP and the Document Info dictionary) and attached to the PDF object. The PDF must still be saved. If an exception occurs in the block, changes are discarded.

In [4]: with pdf.open_metadata() as meta:
   ...:     meta['dc:title'] = "Let's change the title"
   ...: 

The list of available metadata fields may be found in the XMP Specification.

Removing metadata items

Use del meta['dc:title'] to delete a metadata entry. To remove all of the XMP metadata, use del pdf.Root.Metadata.

Checking PDF/A conformance

The metadata interface can also test if a file claims to be conformant to the PDF/A specification.

In [5]: pdf = pikepdf.open('../tests/resources/veraPDF test suite 6-2-10-t02-pass-a.pdf')

In [6]: meta = pdf.open_metadata()

In [7]: meta.pdfa_status
Out[7]: '1B'

Note

Note that this property merely tests if the file claims to be conformant to the PDF/A standard. Use a tool such as veraPDF to verify conformance.

Notice for application developers

If you are using pikepdf to create some kind of PDF application, you should update the fields xmp:CreatorTool and pdf:Producer. You could, for example, set xmp:CreatorTool to your application’s name and version, and pdf:Producer to pikepdf. Refer to Adobe’s documentation to decide what describes the circumstances.

This will help PDF developers identify the application that generated a particular PDF and is valuable debugging information.

Low-level XMP metadata access

You can read the raw XMP metadata if desired. For example, one could extract it and edit it using the full featured python-xmp-toolkit library.

In [8]: xmp = pdf.root.Metadata.read_bytes()

In [9]: type(xmp)
Out[9]: bytes

In [10]: print(xmp.decode())
<?xpacket begin='' id='W5M0MpCehiHzreSzNTczkc9d'?>
<x:xmpmeta xmlns:x="adobe:ns:meta/">
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <rdf:Description xmlns:dc="http://purl.org/dc/elements/1.1/" rdf:about="">
      <dc:creator>
        <rdf:Seq>
          <rdf:li>veraPDF Consortium</rdf:li>
        </rdf:Seq>
      </dc:creator>
    </rdf:Description>
    <rdf:Description xmlns:xmp="http://ns.adobe.com/xap/1.0/" rdf:about="" xmp:CreatorTool="veraPDF Test Builder" xmp:CreateDate="2015-03-10T17:19:21+01:00" xmp:ModifyDate="2015-03-10T17:19:21+01:00"/>
    <rdf:Description xmlns:pdf="http://ns.adobe.com/pdf/1.3/" rdf:about="" pdf:Producer="veraPDF Test Builder 1.0 "/>
    <rdf:Description xmlns:pdfaid="http://www.aiim.org/pdfa/ns/id/" rdf:about="" pdfaid:part="1" pdfaid:conformance="B"/>
  </rdf:RDF>
</x:xmpmeta>
<?xpacket end='w'?>

Editing XMP with a generic XML library is probably not worth the trouble; the semantics are fairly complex.

Warning

Manually changes to XMP stream object will not be synchronized with live PdfMetadata object or the DocumentInfo block.

The Document Info dictionary

The Document Info block is an older, now deprecated object in which metadata may be stored. The Document Info is not attached to the /Root object. It may be accessed using the .docinfo property. If no Document Info exists, touching the .docinfo will properly initialize an empty one.

Here is an example of a Document Info block.

In [11]: pdf = pikepdf.open('../tests/resources/sandwich.pdf')

In [12]: pdf.docinfo
Out[12]: 
pikepdf.Dictionary({
  "/CreationDate": "D:20170911132748-07'00'",
  "/Creator": "ocrmypdf 5.3.3 / Tesseract OCR-PDF 3.05.01",
  "/ModDate": "D:20170911132748-07'00'",
  "/Producer": "GPL Ghostscript 9.21"
})

It is permitted in pikepdf to directly interact with Document Info as with other PDF dictionaries. However, it is better to use .open_metadata() because that interface will apply changes to both XMP and Document Info in a consistent manner.

You may copy from data from a Document Info object in the current PDF or another PDF into XMP metadata using load_from_docinfo().