I've also found that it's really easy to convert D&D 3.x and PF1 modules to the system. Not so easy that thought and care doesn't need to be put into it, but most creatures are based off of the 3e monsters, and there's a similar philosophy of DC adjustments. So, you get both Paizo's catalogue of well designed adventure books, as well as a massive back catalogue of classic favourites that you can dig out for a relatively modest effort.