How to delete all files with specific extension?

You need to get all the files in the directory that match the extension first, then delete each one.

string[] directoryFiles = System.IO.Directory.GetFiles(path, "*.tempfile");
foreach (string directoryFile in directoryFiles)
{
   System.IO.File.Delete(directoryFile);
}

You will first need to use Directory.GetFiles method to get all the files with given extension. Like this:

string[] filesToDelete = Directory.GetFiles("c:\\test", "*.txt");

Then, if you are using .Net 3.0 or higher, you can use this:

filesToDelete.ToList().ForEach(file => File.Delete(file));

Or loop through the array elements and delete each item one by one. A loop would be better since it would let you handle the cases where you do not have rights to delete a file or if the file is in use.