I note this script takes two existing PDFs as an input and produces two new PDFs that collide with each other as output, but they do not collide with either of

I note this script takes two existing PDFs as an input and produces two new PDFs that collide with each other as output, but they do not collide with either of the originals. Thus this does not enable the obvious attack of creating a PDF that contains different text but collides with an existing PDF that you do not control. It does enable some other forms of duplicity, but only if you are the source of both documents.