Support for PDF metadata will be provided in samples/exiv2json.cpp
In v0.25, I added deeply recursive JSON support for XMP. A PDF file is another deeply recursive data structure - which can be self referencing. We have a long term goal to support types of metadata in addition to the existing Exif/IPTC/XMP. I am wondering if JSON may be a better format in which to express metadata. I'm going to add PDF support to exiv2json.cpp to investigate this matter further. I intend to use the podofo library to read and parse PDF. I made a little start on this by building the podofo library and sample applications. I worked for Adobe for many years and very familiar with the structure of PDF files.