How to display content of a file on web

Hi I am new to web development and looking for a way to display content of a file on a web page. Currently I am able to load the content of a text file and show the same in a huge text box. I need to display the content of more types of files like xml or PDF or Excel or infact any types of file. Is there a tag or a plug-in I can use to do so? Also, is there a way I can display content of two documents side by side and provide diff sort of functionality.