Assimil sell a standalone, official PDF of its main 100-lesson coursebook. The digital version of the full course is the interactive e-course application, not a simple PDF file.
Because Assimil handles grammar lightly, pair the course with a free, structured resource like Talk To Me In Korean or How to Study Korean when you need a deeper explanation of a specific verb ending.
To support the creators and ensure you get high-quality materials, consider these legitimate digital routes:
Extract new vocabulary or entire sentences from your daily Assimil lessons and input them into a spaced repetition system (SRS) to prevent forgetting.