How did your friend do it?
Did he write the LaTeX code in Notepad, copy the code into a LaTeX editor, and then copy the displayed equation into yet another application before converting it into a PDF?
What software are you using to write your documents?
If you are using Word, you might have to save the equation as a graphic and then embed the image in your Word document, and then publish it as a PDF document.
Perhaps other members will have other suggestions.