title: apache solr Index pdf files with xml documents
body: <p>how to index pdf files in apache solr (version 8) with xml Documents
  example:</p>
  
  <pre><code>&lt;add&gt;
  &lt;doc&gt;
  &lt;field name="id"&gt;filePath&lt;/field&gt;
  &lt;field name="title"&gt;the title&lt;/field&gt;
  &lt;field name="description"&gt;description of the pdf file&lt;/field&gt;
  &lt;field name="Creator"&gt;jhone doe&lt;/field&gt;
  &lt;field name="Language"&gt;English&lt;/field&gt;
  &lt;field name="Publisher"&gt;Publisher_name&lt;/field&gt;
  &lt;field name="tags"&gt;some_tag&lt;/field&gt;
  &lt;field name="is_published"&gt;true&lt;/field&gt;
  &lt;field name="year"&gt;2002&lt;/field&gt;
  &lt;field name="file"&gt;path_to_the_file/file_name.pdf&lt;/field&gt;
  &lt;/doc&gt;
  &lt;/add&gt;
  </code></pre>
  
  <p>UPDATE</p>
  
  <p>how to set <code>literal.id</code> to filePath</p>