UngeheuerLich
Legend
Pathfinder 1e is a really good improvement on 3.5. It simplifies some issues with skills and cross-class skills, improves a number of classes. Plus, all of its rule additions are available for free at d20PFSRD.
But if you prefer PDFs, Paizo has all of the rulebooks for sale. They‘re quite convenient if you run from a tablet or laptop.
That depends heavily on what you feel what is an improvement.
I for my part see it as fix for the gameplay I would want to avoid (regarding skills).