title: Solr add and update pdf files
body: <p>I want to add and update pdf files to solrs index.
  My scenario: I have a directory (mainDir), which should be indexed. This directory contains many subdirectories with pdf files. New pdf files and subdirectories can be created, updated or deleted.</p>
  
  <p>I already created an Data Import Handler, which indexes all files in my directory recursive. Here's my config:<br></p>
  
  <pre><code>&lt;dataConfig&gt;
    &lt;dataSource type="BinFileDataSource"/&gt;
    &lt;document&gt;  
      &lt;entity name="file" 
              processor="FileListEntityProcessor" 
              dataSource="null" 
              fileName=".*pdf" 
              rootEntity="false" 
              baseDir="/mainDir" 
              recursive="true" &gt;
  
              &lt;field column="file" name="fileName"/&gt;
              &lt;field column="fileAbsolutePath" name="fileAbsolutePath"/&gt;
              &lt;field column="fileDir" name="fileDir"/&gt;            
  
          &lt;entity name="pdf" processor="TikaEntityProcessor" url="${file.fileAbsolutePath}" format="text"&gt;
  
              &lt;field column="title" name="title"/&gt;
              &lt;field column="text" name="_text_"/&gt;
  
          &lt;/entity&gt;     
      &lt;/entity&gt;   
    &lt;/document&gt;
  &lt;/dataConfig&gt;
  </code></pre>
  
  <p>I ran the DIH, it worked, but I have no idea how to add/ update a single pdf file.
  What is the best way to commit changes to the index. Later a node.js API should notice solr about changes.</p>