How can I search multiple phrases within a pdf by javascript?

There's no simple way of doing it, as JavaScript can only read one word at a time from a page, and has no built-in search command it can use. You would need to read the entire contents of the file to a string variable, and then use a Regular Expression to search that string for matches of the phrase you want to look for. If the file is very large this might be problematic to do, though.