VB.Net or C# are going to be your best options. You'll want to learn WPF and XAML to create a simple desktop application with file dialogs and the like. See this similar question:
http://stackoverflow.com/questions/1...arning-wpf-net.
Also, depending on what you plan to do with those files, Excel and PowerPoint integration can be pretty involved. You are going to be working with the Microsoft.Office.Interop libraries (
http://msdn.microsoft.com/en-us/library/15s06t57.aspx). You might learn more than you ever cared to know about the structure of office documents.