title: Possible encoding issues with PDFDocument
body: <p>I am using PDFKit in a Mac app (Xcode 11.7, 10.15 deployment target)  to view pdfs. Users are able to highlight selections and either copy the text, or create quotes.</p>
  <p>With some pdfs, I cannot get the correct string contents for the highlight.</p>
  <p>Take the following pdf: <a href="https://www.irs.gov/pub/irs-pdf/iw8bene.pdf" rel="nofollow noreferrer">https://www.irs.gov/pub/irs-pdf/iw8bene.pdf</a>. If it is opened in Preview, it is possible to copy and paste contents into TextEdit, for example.</p>
  <p>If I open this pdf with PDFView, only some text can be copied and pasted (the main heading for example), but body text only pastes the copied spaces! I have no custom code to handle copy on my PDFView.</p>
  <p>If I evaluate the current PDFSelection when the document is highlighted, I get spaces, and nonsense characters in the string:</p>
  <pre><code>for character in pdfSelection.string!.unicodeScalars {
      print(character.value)
  }
  </code></pre>
  <p>Example result:</p>
  <pre><code>32
  1113109
  1113135
  1113135
  1113109
  32
  1113118
  1113091
  32
  </code></pre>
  <p>Whatever is wrong, the standard copy code is falling foul of it too, so perhaps there is some set-up issue on PDFView or PDFDocument that I am missing? I simply create a PDFView in Interface Builder, then open a PDFDocument with a URL and set it on the view.</p>