[mike.pinkman]

exiftool config

%Image::ExifTool::UserDefined = (
    'Image::ExifTool::XMP::pdfx' => {
        calibre => {
            SubDirectory => {
                TagTable => 'Image::ExifTool::UserDefined::calibre',
            },
        },
    },
);
%Image::ExifTool::UserDefined::calibre = (
    GROUPS        => { 0 => 'XMP', 1 => 'XMP-calibre' },
    NAMESPACE     => { 'calibre' => 'calibre' },
    WRITABLE      => 'string',
    Series => { Writable => 'string' },
	SeriesSeries_index => { Writable => 'string' },
    TagsList => { },
    LastKeywordXMP => { },
    HierarchicalSubject => { },
    CatalogSets => { },
    Subject => { },
);

add metadata

exiftool -config customtest.config Lua.pdf -XMP-calibre:Series="Test"

but it not work, what's wrong with this method?