OleDbConnection can handle structured storage as long as the appropriate OLE DB driver is installed on the machine your app is running on.
Excel:
Provider=Microsoft.ACE.OLEDB.12.0;Data Source=c:\myFolder\myExcel2007file.xlsx;
Extended Properties="Excel 12.0 Xml;HDR=YES";
Text:
Provider=Microsoft.Jet.OLEDB.4.0;Data Source=c:\txtFilesFolder\;
Extended Properties="text;HDR=Yes;FMT=Delimited";
ConnectionStrings.com has a whole host of other Data Sources that you can access via OLE with the built-in libraries.