To change the metadata on an epub, you have to change it in calibre then do save to disk or send to device.
Try doing the same thing with pdf. It might work. Also, it might generate an .opf file with the pdf that will carry the metadata.
There is a thread about it here:
https://www.mobileread.com/forums/showthread.php?t=45045
If you're still not sure, I suggest you post a thread in the calibre section, asking something like 'How do I update pdf metadata from Calibre?'
Also, this:
https://www.mobileread.com/forums/showthread.php?t=83714
It might work, it might not. Good luck!