title: Digital Sign PDF File with PHP and laravel
body: <p>Hello i search a lot before make this question. 
  I know there is a paied option to sign pdf setasign.com </p>
  
  <p>I try to use php function:</p>
  
  <pre><code>openssl_pkcs7_sign( FULL_PATH . "/pdforiginal.pdf", //ORIGIANL PDF
                      FULL_PATH ."signedPDF.pdf", // SIGNED PDF
                      "file://" . FULL_PATH . "signing_cert.pem", 
                       array(  "file://" . FULL_PATH. "private_key.pem",""),array()); 
  </code></pre>
  
  <p>signing_cert.pem &lt;- // I Dont understand what is this i just have private_key and public_key. I see some examples where people use private_key here.</p>
  
  <p>My private key dont have password shoud i use blank "" or null ? </p>
  
  <p>If anyone can give me little information about this topic would be really helpful. </p>