title: Find characters and rename file name using Powershell
body: <p>I have a large number of files in a directory with this type of naming convention:  "1050_14447_Letter Extension.pdf", etc.  I need to remove all characters before the 2nd underscore (including the 2nd underscore).  So the new file name would be "Letter Extension.pdf".  How can I iterate the single directory renaming accordingly?</p>