title: Calculate MD5 checksum for a file
body: <p>I'm using <a href="https://en.wikipedia.org/wiki/IText" rel="noreferrer">iTextSharp</a> to read the text from a PDF file. However, there are times I cannot extract text, because the PDF file is only containing images. I download the same PDF files everyday, and I want to see if the PDF has been modified. If the text and modification date cannot be obtained, is a <a href="http://en.wikipedia.org/wiki/MD5" rel="noreferrer">MD5</a> checksum the most reliable way to tell if the file has changed? </p>
  
  <p>If it is, some code samples would be appreciated, because I don't have much experience with cryptography.</p>