What is PDF Metadata?
In the context of PDFs, metadata refers to the additional information that is embedded within a PDF file.
PDF files have two types of metadata.
The first is called the Document Information Dictionary, which includes details like the author's name, the document title, and the creation and update dates. It's optional and can be added to the file.
The second type is Metadata Streams, introduced in PDF 1.4, which use a standard called Extensible Metadata Platform (XMP) to include additional information in XML format. This can include details about images, fonts, and the entire document.
Metadata helps organize and categorize PDF files, making it easier to search for specific documents. It also supports better management and retrieval of information, especially in large collections of PDF files.
It is possible to add or edit metadata using PDF editing software or tools designed for managing PDF metadata. Using metadata helps improve document organization, searchability, and document workflows.
Given how often PDFs appear in search results, ensuring that your PDF documents have relevant metadata can significantly improve their visibility and click-through rates.
Where a PDF stores its metadata
In two places. The document information dictionary is the older of the two and holds a short fixed list: title, author, subject, keywords, the creating application, the producer, and the creation and modification dates. XMP is the newer: an extensible XML packet that can hold all of that and much more, and is the form preferred by PDF 2.0.
Both can be present and they can disagree, particularly after a file has passed through several tools. Different viewers read different ones, which is why the author shown in one application is sometimes not the author shown in another.
Metadata travels further than you expect
Metadata is written automatically and is rarely reviewed. A document exported from an office suite routinely carries the author's name, their organization, the software and its version, and a full set of timestamps.
None of it is visible on the page, and all of it is shared when the file is. Before publishing a document it is worth reading the metadata and removing what should not travel with it. Note that stripping metadata is separate from removing content: it does not touch anything on the page, and it does not remove earlier revisions left behind by an incremental update.