Redmine

Hi, my Redmine has never shown the option to export to PDF. I don't know if it should be enabled/active by default after installaion.
However I see the vendor/plugins/rfpdf/ so I expect it should work "out of the box".

Versions:
- Redmine 2791
- Rails 2.2.2
- Debian Lenny (5.0) 64 bits
- Ruby 1.8.7

Do I need to install some gem to get "export to PDF" working?

Thanks for any help.