Discovering metadata about a PDF

One of the canonical tools for this is pdfinfo, which comes with xpdf, if I recall. Example output:

[0 1017 17:10:17] ~/temp % pdfinfo test.pdf
Creator:        TeX
Producer:       pdfTeX-1.40.14
CreationDate:   Sun May 18 09:53:06 2014
ModDate:        Sun May 18 09:53:06 2014
Tagged:         no
Form:           none
Pages:          1
Encrypted:      no
Page size:      595.276 x 841.89 pts (A4)
Page rot:       0
File size:      19700 bytes
Optimized:      no
PDF version:    1.5

Another utility worth looking into is exiftool. It might not be the right tool in your specific case as it doesn't report any information on the geometry of the document but in general it is probably the most feature-complete tool for inspecting PDF metadata.

Here's an example of a command that will print all available meta information (-a), sorted by groups (-G1):

exiftool -a -G1 "$File"

The official documentation offers an overview of the supported PDF-related tags:

• PDF Tags
• XMP PDF tags
• XMP dc tags

You can install exiftool on Debian/Ubuntu with:

sudo apt-get install libimage-exiftool-perl

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If you are more into the GUI side of things you could give my project PDFMtEd a try. It's a set of tools that serve as graphical frontends to exiftool and allow viewing and editing PDF metadata.

Here are a couple of screenshots: