Yeah, it changes the game when you need to fill out a pre-existing PDF form with user-supplied data (as opposed to free form PDF generation). In my experience, you pretty much have to use a Java library (such as iText) for this. So for a Rails app, that means JRuby, queue to a Java daemon processor, or something along those lines.

Though I see they're using the prawn gem to do it here: https://github.com/democrats/voter-registration/blob/master/...

Last time I checked, prawn wasn't quite powerful enough for this use case. I'll have to revisit that approach.