title: Displaying PDF files in shiny app doesn't work for all OS and browsers
body: <p>I have developed a shiny app which basically just displays pdf files. This works like a charm on my Mac within Safari browser, but for example not within OSX Firefox. 
  On Windows it doesn't seem to work at all for IE (or Edge) or Firefox.
  One colleague tested it on Linux and it works in Firefox and Chrome.</p>
  
  <p>Here it the link to the shiny app <a href="https://butterlab.imb-mainz.de/EvoAnnotate/" rel="nofollow noreferrer">https://butterlab.imb-mainz.de/EvoAnnotate/</a></p>
  
  <p>Does anyone has a suggestion what I could do? I would prefer to display the PDFs compared to PNG for example, because the file size is much bigger for PNG and the resolution is always limited.</p>
  
  <p>As a reproducible example, here is some code. It expects to have a file called <code>test.pdf</code> in the working directory.</p>
  
  <pre><code>ui &lt;- shiny::fluidPage(
    imageOutput("myImage")
  )
  server &lt;- function(input, output, session) {
    output$myImage &lt;- renderImage({
      list(src = 'test.pdf',
           contentType = 'application/pdf',
           width = 960,
           height = 680,
           alt = 'test.pdf')
    },
    deleteFile=FALSE)
  }
  shinyApp(ui = ui, server = server)
  </code></pre>
  
  <p><strong>EDIT:</strong></p>
  
  <p>I created now for all PDF files a png version and provide a switch for the user, in case the PDF isn't displayed. Not the best solution, but Maybe someone can suggest something more interactive? Maybe using javascript to check if the file is displayed?</p>