The info you provided are vague.
If you 'text file' is a
CSV
then you may parse it yourself, it is not a daunting task.
On the other end if it is in the 'native' excel format (i.e.
Office Open XML - Wikipedia[
^]) then it isn't textual, is binary and you'd probably better use
Excel
automation. Check out this
Code Project
article:
Working with Excel Using C#[
^].