parameter is not of type 'Blob'

To save the File content in innerHtml, you must first read the file. loadend event fires only when file is fully read, and you can access its content without errors:

var reader = new FileReader();
var fileToRead = document.querySelector('input').files[0];

// attach event, that will be fired, when read is end
reader.addEventListener("loadend", function() {
   // reader.result contains the contents of blob as a typed array
   // we insert content of file in DOM here
   document.getElementById('file').innerText = reader.result;
});

// start reading a loaded file
reader.readAsText(fileToRead);

You can read more here - and here

You've made a couple of errors.

The one that the error message is complaining about is that you are trying to select a file using a hard coded string. You cannot determine which file gets loaded. The File API will only allow you to read files that are selected by the user via a File input.

The second is that you are trying to read the result property of the reader before you've read the file. You need an event handler to do that (because file reading, like Ajax, is asynchronous).

document.getElementById("myBtn").addEventListener("click", function() {

  var reader = new FileReader();
  reader.addEventListener('load', function() {
    document.getElementById('file').innerText = this.result;
  });
  reader.readAsText(document.querySelector('input').files[0]);

});

<input type="file">
<button id="myBtn">Try it</button>
<pre id="file"></pre>