The Annotated Vernacular Edition of the “Sūtra on the Profound Gratitude Owed to Parents” (abbreviated as "Phật thuyết") was long believed to have been lost, sharing the fate of most Vietnamese textual materials from before the sixteenth century. Fortunately, in 1979, the Hán–Nôm scholar Tạ Trọng Hiệp, a Vietnamese researcher based in France, brought a copy of this annotated edition back from Paris to Vietnam. The text itself is a Buddhist scripture centering on the virtue of filial piety (hiếu), making it especially valuable to scholars of religious history, intellectual history, and cultural history—particularly those studying Vietnamese Buddhism during the Lê Sơ period, when Confucianism was at its height. In her study of this annotated edition, Hoàng Thị Ngọ classified the structural types of early Nôm characters, focusing on those compounds that employ two distinct graphs to represent a single Vietnamese syllable. She then analyzed the phonological, lexical, and grammatical features of Vietnamese reflected in the text, offering preliminary observations on the translator’s methods. After transcribing and annotating the entire scripture, Hoàng Thị Ngọ also compiled a lexical index with quantitative data on the frequency of native Nôm words and their contextual usage. The study additionally provides readers with a facsimile of the original annotated text, a rare and invaluable document that facilitates further philological and comparative research in multiple disciplinary directions.