Approximately twice a year, Humble Bundle runs a "Pathfinder 2e" bundle. For a $25 donation to charity, you can get a library of worth over $500. These bundles usually include the Core Rulebook, Bestiary 1, the Gamemastery Guide, and about six Adventure Path volumes. This is the most economical way to build a digital collection overnight.
In 2023, Paizo launched the "Remaster" project to move away from the Open Game License (OGL) and toward the ORC License. This resulted in the new Core books mentioned above. If you own the older "Pathfinder Core Rulebook" or "Bestiary" PDFs, they are still compatible with the game, but the new Remaster PDFs offer streamlined rules and cleaner formatting.
Furthermore, the upcoming Pathfinder 2e Remastered Player Core 2 PDF (releasing July 2024) will feature "live" character sheets within the PDF. You will type your level and stats into boxes inside the PDF, and it will auto-calculate your AC and saving throws.