CLI solution
Another utility worth looking into is exiftool. The advantage exiftool holds over pdfinfo is that it supports a lot more metadata types (e.g. XMP tags).
Here's an example of a command that will print all available meta information (-a), sorted by groups (-G1):
exiftool -a -G1 "$File"
Overviews of the supported PDF-related tags:
You can install exiftool on Ubuntu with:
sudo apt-get install libimage-exiftool-perl
GUI solution
If you are looking for a GUI PDF metadata viewer/editor you could give PDFMtEd a try. It's a a set of graphical utilities I wrote for managing PDF metadata with exiftool:

