PDF This is the most popular file format for multipage electronic documents. There are several applications that can produce files in this format, above all Acrobat® and other Adobe® programmes. While Acrobat and its PDF-writer allow you to enter the basic meta data (title, author, subject and keywords) which it also lists in its advanced meta data viewer as appropriate DC-elements, DC-terms are not supported, albeit they are recognized/tolerated if correctly entered with third-party tools such as digi-libris Reader.
It also includes its own XMP set of meta data, but no tool to easily manipulate these within Acrobat itself. All you can do is export/import all advanced meta tags to/from an *.XMP sidecar file.
Another issue with PDF is encryption and password protection. While digi-libris can read the basic four tags in most cases, it may not be able to decipher any other metadata they may contain unless the metadat is attached, e.g. as and XMP sidecar file (see also under blog about dMeta).
Suitable software can extract from, modify and update open PDF files with both DC-elements, DC-terms, citation relevant tags and custom attribute/value pairs as well as other any other well defined schema (DICOMED, IPTC, TIFF etc.).