If you are serious about guitar making—not just dabbling but truly understanding resonance—buying the physical set is a rite of passage. At $295-$350 (depending on supplier, e.g., Luthiers Mercantile International or StewMac), it is expensive. But consider:
Moreover, Somogyi used the profits from the books to fund his teaching workshops and scholarship programs for young makers. Buying the book legitimately keeps the craft alive.
Somogyi’s methods are so unique that many hobbyists believe the PDF contains a "cheat code" to building million-dollar guitars. They want the exclusive, raw data—the deflection numbers, the thickness percentages, the voicing techniques—without paying the masterclass fees.
If you refuse to pay, don't steal. Go to your local public or university library. Request The Responsive Guitar via Interlibrary Loan. Many university music departments have the Somogyi set in their reference section. You can legally scan individual chapters for personal study under Fair Use.