The README states:

full documentation/demos at: http://cracklabs.com/prawnto

However, cracklabs.com is currently parked by GoDaddy.

ActionView::TemplateError: You have a nil object when you didn't expect it! The error occurred while evaluating nil.downcase

class Prawnto::TemplateHandler::CompileSupport
    def ssl_request?
        @controller.request.env['SERVER_PROTOCOL'].downcase == "https"
    end
end

to

class Prawnto::TemplateHandler::CompileSupport
    def ssl_request?
        @controller.request.env['SERVER_PROTOCOL'].to_s.downcase == "https"
    end
end