If you are looking for the digital versions to use alongside the physical book, here are the legitimate resources:
The PDF often provides one example sentence. That is insufficient. For each new high-frequency word, use a Korean dictionary (like Naver Dictionary) to find three new example sentences. Write them in a notebook. If you are looking for the digital versions
The number 6,000 can be intimidating. Break it down. If you are looking for the digital versions