Invest $30–$40 in the Kindle versions of the three N5 books. That is the cost of two pizzas or three coffees. Your Japanese learning journey is worth that small investment.
File-sharing websites are notorious for malware. That "N5 PDF.exe" file is not a PDF—it is a virus. Always be careful.
An "interesting paper" on (Japanese Language Proficiency Test preparation) typically explores why this specific series is a staple for beginners.