wordFormatter.gs

// Add a custom menu item to the document when opened.
function onOpen() {
  var ui = DocumentApp.getUi()
    .createMenu('Set Fonts')
    .addItem('Run','setFont')
    .addToUi();
}

function setFont(){
  var doc = DocumentApp.getActiveDocument();
  var body = doc.getBody();
  
  // Get the doc content
  var elements = body.getParagraphs();

  // Loop through the paragraphs
  for(var i = 0; i < elements.length; i++) {
    
    // Font and style arrays
    var fonts = ['Open Sans','Josefin Slab','Arvo','Lato','Vollkorn','Abril Fatface','Ubuntu','PT Sans','PT Serif','Old Standard TT','Droid Sans'];
    
    // Each word is grown to 48px font size
    // Bold is set with a random boolean value generated for each word
    var style = {};
    style[DocumentApp.Attribute.FONT_SIZE] = '48';
    style[DocumentApp.Attribute.BOLD] = !!Math.floor(Math.random() * 2);
    

    // Choose a random font from the font array
    var font = fonts[Math.floor(Math.random()*fonts.length)];
    
    // Apply the font family and styles to all paragraphs in the document.
    elements[i].editAsText().setFontFamily(font).setAttributes(style);
    
  }
}