title: RegEx for extracting number from a string
body: <p>I have a bunch of files in a directory, mostly labled something like...</p>
  
  <p>PO1000000100.doc or .pdf or .txt
  Some of them are PurchaseOrderPO1000000109.pdf</p>
  
  <p>What i need to do is extract the PO1000000109 part of it. So basically PO with 10 numbers after it...
  How can I do this with a regex?</p>
  
  <p>(What i'll do is a foreach loop on the files in the directory, get the filename, and run it through the regex to get the PO number...)</p>
  
  <p>I'm using C# - not sure if this is relevant.</p>