The aim of the Internal Viewer is to display any file as quickly as possible in Text or Hex view mode. It reads only the parts of the file that are displayed or used to calculate the vertical scroll limit. This means that you can view a 200 GB file at the same speed as a 200 KB file (assuming that it will display the same part of both files).
You can use the Internal Viewer to view a file's contents as text (the Text view mode) or as hexadecimal values (the Hex view mode); search for text or match regular expressions; copy blocks of text to the clipboard or to disk; convert text using a chosen code page; and perform other tasks.