title: Collapse Bookmarks using PYPDF2
body: <p>When I use PYPDF2 to merge two PDF documents, I set the Page Mode to /UseOutlines so that the PDF will display the bookmark pane when the document is opened. </p>
  
  <pre><code>merger = PdfFileMerger()
  merger.append(PdfFileReader(filename,'rb'),import_bookmarks=True)
  merger.setPageMode('/UseOutlines')
  merger.setPageLayout('/SinglePage')
  </code></pre>
  
  <p>However, whenever the PDF document is opened the bookmarks are always expanded. Is there a property that I can modify to force the bookmarks to be collapsed when the document is opened?</p>