title: Merge certain pdf pages in one pdf with pdftk
body: <p>I have some pdf files </p>
  
  <ul>
  <li>Lettera_Contributi_201701-1.pdf</li>
  <li>Lettera_Contributi_201701-2.pdf</li>
  <li>Lettera_Contributi_201701-3.pdf</li>
  <li>so on...</li>
  </ul>
  
  <p>and I'd like to merge only their 2nd pages in one pdf file. I've tried the following pdftk command with a list of file example</p>
  
  <pre><code>pdftk *.pdf cat 2 output test.pdf
  </code></pre>
  
  <p>but the result I get in test.pdf is just the a.pdf's 2nd page..
  Any ideas? </p>
  
  <pre><code>$ pdftk *.pdf cat 2 output test.pdf verbose
  Command Line Data is valid.
  
  Input PDF Filenames &amp; Passwords in Order
  ( &lt;filename&gt;[, &lt;password&gt;] ) 
     Lettera_Contributi_201701-1.pdf
     Lettera_Contributi_201701-2.pdf
     Lettera_Contributi_201701-3.pdf
     Lettera_Contributi_201701-4.pdf
     Lettera_Contributi_201701-5.pdf
     Lettera_Contributi_201701-6.pdf
  
  The operation to be performed: 
     cat - Catenate given page ranges into a new PDF.
  
  The output file will be named:
     test.pdf
  
  Output PDF encryption settings:
     Output PDF will not be encrypted.
  
  No compression or uncompression being performed on output.
  
  Creating Output ...
     Adding page 2 X0X  from Lettera_Contributi_201701-1.pdf
  </code></pre>