Older versions of Assimil Thai were criticized for using mostly romanization (phonetic English/French letters) instead of the actual Thai script in the main dialogues. Check that your version includes the script if you want to master reading.
While I couldn't find a direct downloadable PDF of the Assimil Thai course, you can try the following: assimil thai pdf
The Thai language presents unique challenges for English speakers: a tonal system, a non-alphabetical script, and no spaces between words. The (Thai sans peine) series is highly coveted because: Older versions of Assimil Thai were criticized for
Assimil Thai is a language learning course designed for beginners to learn the Thai language. The course is part of the Assimil series, a well-known language learning system that focuses on intuitive and immersive learning. a non-alphabetical script