PDF metadata is information embedded in a PDF file that describes the document rather than being part of its visible content. Standard PDF metadata includes: Title, Author, Subject, Keywords, Creator (application that created it), Producer (application that converted to PDF), creation date, and modification date. This metadata is stored in two places: the Document Information Dictionary (legacy) and XMP (Extensible Metadata Platform) metadata packets.
Privacy concerns: PDF metadata can unintentionally reveal sensitive information. Author field contains the real name associated with the software license. Creator field reveals which software was used. Revision history can expose previous versions of the document. Some PDFs created in corporate environments contain user account names, company server paths, and tracked changes that weren't intended for external audiences. Legal discovery processes have found sensitive metadata in publicly released PDFs.
Removing metadata: Adobe Acrobat's Document Properties allows editing basic metadata. Acrobat's "Sanitize Document" feature (part of PDF/A workflow) removes all metadata and hidden data. Command-line tools like ExifTool and Ghostscript can strip metadata. Printing a PDF to a new PDF via a PDF printer effectively strips most metadata. Be careful when sharing PDFs externally — inspect metadata first with a viewer or use a dedicated metadata-removal tool.