I have another question. This time I searched in the manual, but didn't find

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Then adding books sometimes (when using read metadata from file) a lot of metadata gets filled in: comments, tags, author, title. This can happen even if I am adding just one pdf file, no opf files in sight.
Can I save to disk a book with metadata, but without opf file? I want to have one nice file but without loosing all my work on metadata. I tried to save a book to disk, delete it from library and to add it again (reading metadata), but only author, title gets filled in.