Is your interest academic/historical or for personal spiritual study?
The Internet Archive hosts a digitised version of the Brahmayamalatantra (Picumata). brahma yamala tantra pdf free
Scholars and practitioners value the Brahma Yamala for several specific reasons: Academic libraries (manuscript archives)
The Brahma Yamala Tantra and The Early Saiva Cult ... - Scribd a leading scholar on this text
Ritual Manuals: The scripture serves as a manual for various rituals.
Academic Translations: Shaman Hatley, a leading scholar on this text, has published extensive research and partial translations. While his full monographs may be under copyright, many of his introductory papers and chapters are available for free on academic platforms like Academia.edu or ResearchGate. A Word of Caution
Significance: It is a massive work of approximately 12,500 verses spanning 104 chapters. It holds critical importance in both Śaktism and Vaiṣṇavism as a primary source for early medieval religious history.