You could find plentiful of information anywhere. For example, you could use Microsoft.Jet:
https://en.wikipedia.org/wiki/Microsoft_Jet_Database_Engine[
^].
Here is one of the code samples:
https://social.msdn.microsoft.com/Forums/vstudio/en-US/a6ceb8be-b633-4fff-88e0-1692206e2db2/c-excel-to-text-conversion[
^].
[EDIT] Another approach is using
Microsoft.Office.Interop.Excel
, and one more would be using Microsoft Open XML SDK. You will find plenty of code samples. [END EDIT]
But I'll repeat: what you are going to do with the text? It looks to me as a non-engineering approach, the attempt of getting a little further from the user-level manual work. The mere fact that someone put the huge amount of data in Excel, office personnel's tool, tell the tail. Please, nothing personal. I could be mistaken here, but your attempt to play the "insult" card only confirms that. If I'm mistaken, just explain that. Anyway, you got the "solution".
—SA