Emilio Pujol's "Escuela Razonda de la Guitarra," according to Pujol's preface to libro cuatro, was conceived as an eventual five-volume work in 1923. Pujol writes that the first book (el primer libro, as Pujol refers to it in the Spanish prefacio) was edited in 1934, the second published in 1940 and the third edited in 1934.
Even though this preface appears in the fourth volume, nowhere in that book does it say exactly when el cuatro libro appeared, though the edition circulating around the internet of *el primero libro" has a 1954 copyright.
The el cuatro libro available on the internet as a PDF has a date on the back cover of March 16, 1998.
All four volumes, originally published by Ricordi in Argentina, have text in both Spanish and French. It is the contention of Matanya Ophee, whose Editions Orphée published the excellent English translation of volumes 1-3, that Pujol wrote the French text in addition to the Spanish and didn't rely on a translator.
There is a preface in libro tercero, dated September 1952, called proemio in Spanish
Also in the prefacio to el cuatro libro is the plan for a fifth volume, which was never been published. Some say it exists in manuscript and will be released at some point, but as of August 2020, it hasn't appeared.
All four of Pujol's "Escuela Razonada" volumes are generally available on the internet in PDF form. Since there is a legitimate publisher, I won't host them here (unless and until I determine that the Melos editions are satisfactory).
The Spanish-French volumes are now published by Buenos Aires-based Melos Ediciones Musicales. Melos offers all four volumes of "La Escuela Razonada de La Guitarra, a book of Pujol compositions and his "El Dilema Del Sonido en La Guitarra," his treatise — with Spanish, French and English text — translated as "The Dilemma of Timbre on the Guitar," which is mostly about whether to use the nails or bare fingers to play the instrument. Pujol comes down on the side of bare fingers, which he said his mentor Francisco Tárrega used later in life.
The prices of the Pujol books on the Melos site seem more than outrageous, But that's because they are priced in Argentine pesos and use the $ sign. No, the books aren't $850 to $1,835 in American dollars. They are hard to find but are in fact available for reasonable prices on Amazon:
"Escuela Razonada de La Guitarra — Libro 1" ($15.99 in 2020)
"Escuela Razonada de La Guitarra — Libro 2" ($15.79 in 2020)
"Escuela Razonada de La Guitarra — Libro 3" ($9.99 in 2020)
"Escuela Razonada de La Guitarra — Libro 4" ($12.99 in 2020)
I haven't seen the Melos editions yet, though I will be ordering at least one of the volumes soon.
The Ricordi editions are VERY valuable to have as references, and they can be found as PDFs in many places on the Internet.
The best is Universidad Panamericana, which offers PDFs of all four "Escuela Razonada" volumes (look at the bottom of the page for the links). This is the easiest way to get them.
Another way is through Scribd.com. You need to start an account, but you don't need to subscribe to the service (and they shouldn't be charging for decades-old PDFs for which they have no ownership). Even if you can't "see" the PDFs on Scribd without a subscription, the Download button still works.
"El Dilema Del Sonido en La Guitarra" is available on Amazon, but at an exorbitant price. Rob MacKillop offers the English portion as a PDF on his excellent web site. A version with Spanish, French and English can be found on Scribd. Unless you really want the Spanish and French versions, Rob's PDF is clearer (in the literal sense).
Universidad Panamericana Campus Mexico PDFs of "Escuela Razonada de La Guitarra" (Links to all four volumes are near the bottom of the page)
Rob MacKillop's Emilio Pujol page
Towards the Holy Grail: A Short History of Guitar Methods by Graham Wade (Classical Guitar Magazine, June 17, 2019)