Unless you are generating the pdf's with cfdocument
and add the image when the files are generated, I think
iText is about as close as it gets. Besides, iText is what
cfdocument uses behind the scenes to generate pdf's anyway.
How many pages does the PDF have? What is the image type,
i.e. jpg, tiff, png? How do you wish to add the image, for example,
on which page(s)? Where on the page is the space you reserve for
the image? For example, what are the coordinates of the top-left
corner of the rectangle?
Another look at your post tells me you probably want to
insert the image on a single page. Here then is some code that
should do it. I have included alternatives, for example, how to
insert the image on every even-numbered page.