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PDF20 Spec 14 Metadata
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14.3 Metadata 14.3.1
General
A PDF document may include general information, such as the document’s title, author, and creation and modification dates. Such global information about the document (as opposed to its actual content or structure) is called document metadata. Beginning with PDF 1.4, it is possible to include metadata for individual objects in a document. Such object-specific metadata is called object-level metadata. Metadata can be stored in a PDF document in the following ways: •
For document data and for object-level metadata: In a metadata stream (PDF 1.4) associated with the document or a component of the document (14.3.2, "Metadata streams"). Metadata streams are the preferred method in PDF 2.0.
•
For document metadata only: In a document information dictionary associated with the document (14.3.3, "Document information dictionary"). Except for the CreationDate and ModDate entries, the use of the document information dictionary for document metadata is deprecated in PDF 2.0.
PDF’s document information dictionaries provided the initial means of including metadata in a PDF file. When metadata streams began to be used in PDF 1.4, XMP was introduced to provide a much richer mechanism to represent metadata entries. Using XMP, a document’s title can be in more than one language or a document’s authors can be represented as a list. Machine-generated metadata for date and time of creation or last modification of a PDF document can adequately be represented in the document information dictionary and in the document’s metadata stream. In some cases document information dictionary entries are required, such as when PieceInfo dictionaries (see "14.5, "Pagepiece dictionaries") are used; they can be present in both the document information dictionary and the document-level metadata stream as needed.
14.3.2
Metadata streams
Metadata, both for an entire document and for objects within a document, can be stored in stream dictionaries (PDF 1.4). These streams are called metadata streams. Besides the entries common to all stream dictionaries (see "Table 5 — Entries common to all stream dictionaries"), a metadata stream dictionary shall contain the additional entries listed in "Table 347 — Additional entries in a metadata stream dictionary".
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Table 347 — Additional entries in a metadata stream dictionary Key
Type
Value
Type
name
(Required) The type of PDF object that this dictionary describes; shall be Metadata for a metadata stream.
Subtype
name
(Required) The type of metadata stream that this dictionary describes; shall be XML.
The contents of a metadata stream shall be the metadata represented in Extensible Markup Language (XML) and the grammar of the XML representing the metadata shall be defined according to the extensible metadata platform specification (ISO 16684-1). A metadata stream representing document-level metadata can be attached to a PDF document through the Metadata entry in the document catalog dictionary (see 7.7.2, "Document catalog dictionary"). A metadata stream representing object-level metadata can be attached to the object through the Metadata entry in a stream or dictionary representing the object or associated with the object (see "Table 348 — Additional entry for components having metadata"). Object level metadata can also be associated with marked-content within a content stream, by including a metadata stream in the property list dictionary for this marked-content. Because a stream dictionary is always an indirect object, a property list containing a metadata stream cannot be encoded inline in the content stream, but needs to be encoded as a named resource (see 14.6.2, "Property lists"). In general, any PDF stream or dictionary may have metadata attached to it as long as the stream or dictionary represents an actual information resource. When there is ambiguity about exactly which stream or dictionary may bear the Metadata entry, the metadata shall be attached as closely as possible to the object that actually stores the data resource described. Table 348 — Additional entry for components having metadata Key
Type
Metadata stream
Value (Optional; PDF 1.4) A metadata stream containing metadata for the component.
NOTE 1
Metadata describing an ICCBased colour space would be attached to the ICC profile stream describing it, and metadata for embedded font files would be attached to font file streams rather than to font dictionaries. Metadata describing a tiling pattern would be attached to the pattern stream’s dictionary, but a shading needs to have metadata attached to the shading dictionary rather than to the shading pattern dictionary that refers to it.
NOTE 2
In tables defining document objects, the Metadata entry is listed only for those document objects in which it is most likely to be used. However, a Metadata entry can appear in other objects as long as those objects are represented as streams or dictionaries.
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14.3.3
Document information dictionary
The Info entry in the trailer of a PDF file (see 7.5.5, "File trailer") is optional. If present it shall hold a document information dictionary (see "Table 349 — Entries in the document information dictionary"). Earlier versions of the PDF file format used the document information dictionary to represent document level metadata. In PDF 2.0 such use is deprecated except for two entries, CreationDate and ModDate. For any other document level metadata, a metadata stream (see 14.3.2 "Metadata streams") should be used instead. Where a document information dictionary contains keys other than CreationDate and ModDate, the value associated with any such key shall be a text string. Document information dictionaries are also used with Threads (see "Table 162 — Entries in a thread dictionary"). Table 349 — Entries in the document information dictionary Key
Type
Value
Title
text string
(Optional; PDF 1.1; deprecated in PDF 2.0) The document’s title. NOTE 1 The dc:title entry in the document’s metadata stream can be used to represent the document’s title.
Author
text string
(Optional; deprecated in PDF 2.0) The name of the person who created the document. NOTE 2 The dc:creator entry in the document’s metadata stream can be used to represent the person or persons who created the document. This note was corrected in this document (2020).
Subject
text string
(Optional; PDF 1.1; deprecated in PDF 2.0) The subject of the document. NOTE 3 The dc:description entry in the document’s metadata stream can be used to represent the subject the document.
Keywords
text string
(Optional; PDF 1.1; deprecated in PDF 2.0) Keywords associated with the document. NOTE 4 The pdf:Keywords entry in the document’s metadata stream can be used to represent the keywords for the document.
Creator
text string
(Optional; deprecated in PDF 2.0) If the document was converted to PDF from another format, the name of the PDF processor that created the original document from which it was converted. NOTE 5 The xmp:CreatorTool entry in the document’s metadata stream can be used to represent the creation tool of the document.
Producer
text string
(Optional; deprecated in PDF 2.0) If the document was converted to PDF from another format, the name of the PDF processor that converted it to PDF. NOTE 6 The pdf:Producer entry in the document’s metadata stream can be used to represent the tool that saved the document as a PDF.
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Key
Type
CreationDate date
Value (Optional) The date and time the document was created, in humanreadable form (see 7.9.4, "Dates"). NOTE 7 The xmp:CreateDate entry in the document’s metadata stream can be used to represent document’s creation date and time.
ModDate
date
(Required if PieceInfo is present in the document catalog dictionary; otherwise optional; PDF 1.1) The date and time the document was most recently modified, in human-readable form (see 7.9.4, "Dates"). NOTE 8 The xmp:ModifyDate entry in the document’s metadata stream can be used to represent the date and time the document was most recently modified.
Trapped
name
(Optional; PDF 1.3; deprecated in PDF 2.0) A name object indicating whether the document has been modified to include trapping information (see 14.11.6, "Trapping support"): True
The document has been fully trapped; no further trapping shall be needed. This shall be the name True, not the boolean value true.
False
The document has not yet been trapped. This shall be the name False, not the boolean value false.
Unknown
Either it is unknown whether the document has been trapped or it has been partly but not yet fully trapped; some additional trapping may still be needed.
Default value: Unknown. NOTE 9 The value of this entry can be set automatically by the software creating the document’s trapping information, or it can be known only to a human operator and entered manually. NOTE 10 The pdf:Trapped entry in the document’s metadata stream can be used to represent the trapping information for the document.
EXAMPLE
This example shows a document information dictionary containing just the creation and last modification date, together with the same document’s metadata stream containing the creation and last modification date and several other document level metadata fields.
101 0 obj %document information dictionary <</CreationDate (D:20140314124211+01'00) /ModDate (D:20140924212303+02'00)
endobj 102 0 obj << /Type /Metadata /Subtype /XML /Length 103 0 R
stream
%document level metadata stream
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="My XMP Tool Kit v3.7"> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="" xmlns:xmp="http://ns.adobe.com/xap/1.0/"> xmp:CreateDate2014-03-14T12:42:11+01:00</xmp:CreateDate> xmp:ModifyDate2014-09-24T21:23:03+02:00</xmp:ModifyDate>
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xmp:CreatorToolMy Word Processor v10.7</xmp:CreatorTool> xmp:MetadataDate2014-09-24T21:23:03+02:00</xmp:MetadataDate> </rdf:Description> <rdf:Description rdf:about="" xmlns:pdf="http://ns.adobe.com/pdf/1.3/"> pdf:ProducerMy Word Processor PDF Exporter Module v2.1</pdf:Producer> </rdf:Description> <rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/"> dc:formatapplication/pdf</dc:format> dc:title rdf:Alt <rdf:li xml:lang="x-default">Annual report 2014</rdf:li> <rdf:li xml:lang="en">Annual report 2014</rdf:li> <rdf:li xml:lang="de">Jahresbericht 2014</rdf:li> </rdf:Alt> </dc:title> dc:creator rdf:Seq rdf:liJohn Doe</rdf:li> rdf:liMary Miller</rdf:li> </rdf:Seq> </dc:creator> </rdf:Description> </rdf:RDF> </x:xmpmeta>
endstream endobj
14.3.4
Reconciling two sources of document metadata
Information about time and date of creation might differ from the most recent modification of a PDF document. If this is the case, the following rules shall apply when writing a PDF document: •
When writing the time and date of creation for the first time, typically when a new document is created, a PDF processor shall ensure that the data in the document information dictionary and the document level metadata stream – if both are written – are fully equivalent.
•
When writing modifications to an existing PDF document, if the PDF document already contains time and date of creation in both the document information dictionary and in the document’s metadata stream, and the two are not equivalent, a PDF processor should leave the inconsistent values unchanged.
•
When writing modifications to an existing PDF document, if the PDF document contains time and date of creation only in the document information dictionary or in the document’s metadata stream but not both, a PDF processor may add the information to the other, as long as both are fully equivalent.
•
When writing the time and date of the most recent modification, typically when an existing document has been modified, a PDF processor shall ensure that the data in the document information dictionary and the document level metadata stream – if both are written – are fully equivalent.
If a PDF processor encounters inconsistent data for time and date of creation or for most recent modification in the document information dictionary and in the document’s metadata stream, it is at the discretion of the PDF processor how to use this data.
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