from http://docs.python.org/download.html and
http://docs.python.org/3.0/download.html you can download the python
documentation in many formats (html, pdf, txt), I think auto-generated
by the .rst source.

While html and txt does not, the pdf format, supports some simple
"meta-data" infos about the document: other than the number of pages,
the page size, the creator, etc... (all auto-filled) there are 4 "keys"
that the current pdf miss to fill and I think it's important: Title,
Subject, Keywords, and Author.

try, for example, to use the simple pdfinfo tool (from
http://poppler.freedesktop.org/) to inspect the current pdf

$ tar xvjf python-3.0.1-docs-pdf-a4.tar.bz2
$ cd docs-pdf
$ ls -1
c-api.pdf
distutils.pdf
documenting.pdf
extending.pdf
howto-advocacy.pdf
howto-cporting.pdf
howto-curses.pdf
howto-doanddont.pdf
howto-functional.pdf
howto-regex.pdf
howto-sockets.pdf
howto-unicode.pdf
howto-urllib2.pdf
howto-webservers.pdf
install.pdf
library.pdf
reference.pdf
tutorial.pdf
using.pdf
whatsnew.pdf
$ pdfinfo library.pdf
Title:
Subject:
Keywords:
Author:
Creator:        LaTeX with hyperref package
Producer:       pdfTeX-1.40.9
CreationDate:   Sat Feb 14 11:33:09 2009
ModDate:        Sat Feb 14 11:33:09 2009
Tagged:         no
Pages:          1077
Encrypted:      no
Page size:      595.276 x 841.89 pts (A4)
File size:      7556857 bytes
Optimized:      no
PDF version:    1.4

erh, what is supposed to contain "using.pdf"? and "distutils.pdf"?

(Yes, I know what they contain, but...)

If the pdf were "tagged", not only me, but also my OS will know what's
in these pdf (see nepomuk/strigi/tracker/beagle programs, helping me
find what I'm searching

I thought we already did assign these metadata items; looks like it's
been messed up somehow.  I'll fix this.

AFAIK, this is obtained using \pdfinfo{} command[1][2][3]

[1] http://theoval.cmp.uea.ac.uk/~nlct/latex/pdfdoc/pdfdoc/pdfdoc.html
[2] http://tex.stackexchange.com/questions/5958/is-hyperref-really-the-best-way-to-add-metadata-to-a-tex-file
[3] http://www.tug.org/applications/hyperref/manual.html#x1-110003.7

Georg, do you think this is something that sphinx has to handle (in the latex builder) or somewhere else?

This seems to be fixed now.  I downloaded python-3.3.1-docs-pdf-letter.tar.bz2 and ran pdfinfo on using.pdf:

Title:          Python Setup and Usage
Subject:        
Keywords:       
Author:         Guido van Rossum, Fred L. Drake, Jr., editor
Creator:        LaTeX with hyperref package
Producer:       pdfTeX-1.40.10
CreationDate:   Fri May 10 09:42:17 2013
ModDate:        Fri May 10 09:42:17 2013
Tagged:         no
Pages:          65
Encrypted:      no
Page size:      612 x 792 pts (letter)
File size:      432316 bytes
Optimized:      no
PDF version:    1.4

We could fill in Subject and Keywords, but the basic fields of Title and Author seem to be present.  (Do we need to change author to 'Python Development Group' or 'PSF'?)

I get the following output when I try Python 3.5.1 docs:

$ pdfinfo using.pdf 
Title:          
Subject:        
Keywords:       
Author:         
Creator:        LaTeX with hyperref package
Producer:       pdfTeX-1.40.14
CreationDate:   Sat Apr  2 00:17:54 2016
ModDate:        Sat Apr  2 00:17:54 2016
Tagged:         no
Pages:          69
Encrypted:      no
Page size:      595.276 x 841.89 pts (A4)
File size:      368343 bytes
Optimized:      no
PDF version:    1.5

The problem seems to have been fixed again somewhere in the past.