You can accomplish this READLINE() and a loop.

Code:

Dim $Line, $Counter
$Counter = 0
Open(1,"File.csv")
Open(2,"Range1.csv",5)
Open(3,"Range2.csv",5)
Open(4,"Range3.csv",5)
$Line = Readline(1)
 While @Error = 0
  Select
    Case $Counter <= 2000
      WriteLine(2, $Line + @CRLF)
      $Counter = $Counter + 1
      $Line = Readline(1)
    Case $Counter => 20001 and $Counter <=4000
      Writeline(3, $Line + @CRLF
      $Counter = $Counter + 1
      $Line = Readline(1)
    Case $Counter >= 4001
      WriteLine(4, $Line + @CRLF)
      $Counter = $Counter + 1
      $Line = Readline(1)
  EndSelect
Loop
Close(1)
Close(2)
Close(3)
Close(4)
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