A: Yes. A corrupted font or missing page in a free PDF will cost you weeks of confusion. Think of the 500 THB as an investment to avoid future headaches. Many Thai libraries (หอสมุดแห่งชาติ) also allow digital borrowing.

The PDF is just a tool. Whether it is verified or not, your effort is what passes the exam. がんばってください (สู้ๆ นะครับ/คะ)!