title: How to fix broken packages in ubuntu?
body: <p>I bought a new laptop and installed Ubuntu on it, I added the touch pad gestures ,and tweaked some other settings like changing the lockscreen wallpaper etc..</p>
  
  <p>Then i wanted to install <strong>Okular</strong> but it shows an error:</p>
  
  <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Some packages could not be installed. This may mean that you have
  requested an impossible situation or if you are using the unstable
  distribution that some required packages have not yet been created
  or been moved out of Incoming.
  The following information may help to resolve the situation:
  
  The following packages have unmet dependencies:
   okular : Depends: libpoppler-qt5-1 (&gt;= 0.62.0-1ubuntu1) but it is not going to be installed
  E: Unable to correct problems, you have held broken packages.
  </code></pre>
  
  <p>And i don't know how to solve this.</p>