[Adoby]

Calibre attempts to update basic metadata. However many PDFs are created in a way that means that this fail.

However when adding, the opf-file should be used to set metadata in calibre. There is an option to read metadata from the filename. Make sure that you don't have this activated, and try again. Also you obviously need to have PDFs together with their individual opf-files. Perhaps you have turned saving opf-files off?

Please also note that PDF isn't the best format to use if you want to make full use of calibre. PDFs usually aren't meant to be changed or updated. Epub, for instance, would be a better choice.