$(document).ready(function() {
var fileTypes = {
  // extension: 'image file'
  doc: '/wp-content/themes/derwentliving/images/icon-word.png',
  xls: '/wp-content/themes/derwentliving/images/icon-excel.png',
  pdf: '/wp-content/themes/derwentliving/images/icon-acrobat.png'
};

// then, loop over the object
// using jQuery's $.each()
$.each(fileTypes, function(extension,image) {
  $('a[href$="' + extension + '"]').
    css({
      paddingLeft: '20px',
      paddingTop: '2px',
      paddingRight: '2px',
      background: 'transparent url("' + image + '") no-repeat center left'
    });
});

});