A primary source is defined as "a document or record containing firsthand information or original data on a topic, used in preparing a derivative work. Primary sources include original manuscripts, periodical articles reporting original research or thought, diaries, memoirs, letters, journals, photographs, drawings, posters, film footage, sheet music, songs, interviews, government documents, public records, eyewitness accounts, newspaper clippings, etc." (Joan M. Reitz, Online Dictionary for Library and Information Science, https://www.abc-clio.com/ODLIS/odlis_p.aspx). What is or is not a primary source can perhaps be better understood by comparison with the definition of a secondary source: "any published or unpublished work that is one step removed from the original source, usually describing, summarizing, analyzing, evaluating, derived from, or based on primary source materials, for example, a review, critical analysis, second-person account, or biographical or historical study. Also refers to material other than primary sources used in the preparation of a written work" (Reitz, https://www.abc-clio.com/ODLIS/odlis_s.aspx).
Buddhadasa Indapanno Archives (BiA) seeks to "collect, maintain and set up a database for original written works by Buddhadasa Bhikkhu, to provide support for education, research, development, publication and exchange of Dhamma knowledge." (website) Buddhadasa, also known as Phra Dharmakosacarya, Phra Thēpwisutthimēthī, or Buddhadasa Indapañño, (May 27, 1906 – May 25, 1993) was a famous and influential Thai ascetic-philosopher of the 20th century.