Console Application

For reading text, look at the textfieldparser class.
For reading and writing csv you can look at http://knab.ws/blog/index.php?/archives/10-CSV-file-parser-and-writer-in-C-Part-2.html (read) and http://knab.ws/blog/index.php?/archives/3-CSV-file-parser-and-writer-in-C-Part-1.html (write).
For xml, you can look at the xmldocument class.
For Excel, do a search on the web; plenty of examples but I currently can't find the one that I want to link to (sorry); note that there probably is a difference between xlxs and xls.