I had assumed you were using Prawnto.
Which version of Rails are you using?
I'm not sure what the issue is with Prawnto and Rails version but why not try to unpack the plugin files to your /lib directory and then run them.
Rails should give you concise enough error messages that you can work out where the issues are and correct them?
Another approach would be to create the .pdf file and use the send_file method to download it to your user?
Thanks for your answer Gavin,
No, it don't helps because I did forget to mention that I do not use Prawnto (because a higher version of rails would be necessary). Or how do I have to name the template?
Any other suggestion?
To display pdfs you'll want to create a view template with extension .pdf.prawn (eg. show.pdf.prawn)
In the corresponding action you then want to respond_to pdf just like you would any other format.
When linking to this file: link_to( "click me", model_path(@model, :format => :pdf ) )
Hope that helps?