df = spark.read.csv("/mnt/lake/data/csv")

Here I assume "/mnt/lake/data/csv" is the directory with the 5 files.
spark.read.csv also has some options like the separator, header etc:
https://spark.apache.org/docs/latest/sql-data-sources-csv.html

So there is no need to do this one by one, read the whole dir in one go.