Noted author and translator of sacred texts Joseph Peterson recently posted the whole text of Raham Asha’s new edition of šak-ud-gumanih-vizar — The Doubt-removing book of Mardanfarrox to http://www.avesta.org/mp/SGV.pdf
archive.org posts this info about the text Asha’s edition stems from:
“There is extant in Parslg literature a controversial book entitled sak-ud-gumanigih-vizar, lit. ‘doubt-removing’ 1 . The author of this book is Mardanfarrox son of Ohrmazddad. Nothing has been found about him elsewhere. He has described himself as a suitor and researcher of truth who did not like to follow a religion by inheritance, but he sought that which is more reliable and acceptable before the philosophy and logic. He claimed to have travelled in many foreign lands and islands, although he only mentioned the name of India. He met many different sects, examined other doctrines, and read other scriptures. He then fell into “the depths of the gloom and ill-solvable doubtfulness”, and it seems that the doctrine of Mani seduced him more, until a time when, owing to the books and memoranda of the wise Magi, he “escaped from much doubtfulness, error and deceit of doctrines.” Mardanfarrox first wrote a small pamphlet that consisted of
a number of inquiries, suggested, in a friendly manner, by a sceptic, a certain Mihrayyar, of Spahan, and answered by him (Chapter one). Thereafter, he determined to write a treatise for removing the doubts of neophytes concerning the Mazdayasnian religion, in contrast with its opponents.
“Mardanfarrox wrote the doubt-removing book from the writings of the previous high-priests, and inserted two chapters of the Denkird, which are not found in the portion of the Denk ir d known to be extant.”