title: how to open all text files from a directory
body: <p>I need peace of code that open all text files from a specific folder and do some process and then save it.
  For example theses are my files  in this folder</p>
  
  <pre><code>MainFolder=&gt;Subfolder1=&gt;Textfile1.txt  
  MainFolder=&gt;Subfolder2=&gt;Textfile1.txt  
  MainFolder=&gt;Subfolder2=&gt;Textfile1.txt 
  </code></pre>
  
  <p>I don't know how to open all Textfile1 files in the MainFolder folder automatically, and do some process and then save them there.</p>