Grabbar,
You have a variety of issues in you question (missing brackets, incorrect calls to Take, referencing indices beyond the last value). Focus first on importing the data:
multilineString = Import["posit.txt", "Text"]
"64817367.784333
1234.566
2345.567
3456.890
123
234
456
"
Then split into lines:
listOfStrings = StringSplit[multilineString]
{"64817367.784333", "1234.566", "2345.567", "3456.890", "123", "234", "456"}
And convert the strings to numbers:
listOfNumbers = Map[ToExpression, listOfStrings]
{6.48174*10^7, 1234.57, 2345.57, 3456.89, 123, 234, 456}
After that you can use the Partition
command to split the data in sets of 4 and then apply your formula.