The Ruby On Rails Wiki lists a couple of libraries that facilitate PDF generation in Rails. I need to print out address labels (in letter f
For your use case, I agree with most other answers that prawn is the right choice because you need pixel-level control over the output.
For generating PDF reports with built-in (opinionated) table styling, headers, etc., you can use the report gem - check out Generate pdf from Rails 3 - what tool to choose? for an example of how to use.