Export From Excel Into .txt file [C#]

Question

Greetings

Dear members, I've been checking out on internet, however, i didn't a single similar question, so i thought to ask it, may come handy for someone else, so here i go:

I have this giant excel files with 2 columns and +800,000 rows, the process is like this:

I am Filtering based on the second column(so there are many similar data on second columns), then after filter, i copy the first column and paste it on a notepad file(.txt) and change its name to second's column filter.

[Summery]

Input: Excel File

Output: multiple Notepad Files .txt

if i do this by hand would take hours and hours, so i thought maybe you can point me into a right direction, then rest i do myself.

Thank you in advance,