There is no subtitle meta tag for pdf in exiftool. Therefore I want to add new exif tag for pdf files, it's name must be PdfSubTitle. To do this, exiftool has a guide page. But I don't understand because my knowledge of perl and exif not enough. Also there is no example for pdf files in the guide. How can I do that?
When everything goes right it should be like:
$ exiftool -config exif.config -PdfSubTitle="Sub Title" file.pdf