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Philosopher - it may come as surprise but, Phil Harvey's exif-tool can edit PDF metadata. Google for it. Oh look - I have bookmarked a blog that refers to it ==>>
PDF metadata: different tool, same story - Ross Mounce Ψ²
To see the non standard properties (series etc) you need something that will show the XML metadata - exiftool will do that
BR
PS : I too have often wished for an option in Add Book that would get metadata from file name as per selected template, and gather anything else from embedded metadata. Would also be good if Extract ISBN functionality could be incorporated into Add Book.