You can find a wide range of Hindi Tantra, Mantra, and Yantra books available for free PDF download on the Internet Archive
मंत्र तंत्र यंत्र विज्ञान अगस्त १९८९ : Ajay Uttam - Internet Archive You can find a wide range of Hindi
Yantra, Mantra Tantra Vidhya : Dediyar, Vladimir : Free Download, Borrow, and Streaming : Internet Archive. Yantra Mantra Kalp Sangrah : Nagori, Chandanmal Here are five legendary books available right now
Many texts on Tantra are "sealed" or intended for initiated practitioners (Dikshita). Academic translations (like those by Woodroffe or David Gordon White) provide the "theory," while the Hindi "Karmkand" books provide the "practice" for priests. Mantra Tantra Vidhya : Dediyar
Here are five legendary books available right now on the Internet Archive for free PDF download. (You can search these exact titles).