Complex sentence: However, there is no need to compare the published text with its alleged source to see that it is inauthentic: no Pope would ever use it, since, if he did, he would certainly be accused of heresy.
Split into simpler sentences: However, there is no need to have recourse to such a comparison to see that the published text is inauthentic. An examination of the text itself is sufficient, since, if a Pope were to use it, he would certainly be accused of heresy.