# 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 may be read, but only scalar quantities can be modified. 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.

## 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.

## 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.

## 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()`.