PDF is not Postscript. If you explain what you're trying to accomplish, someone may be able to suggest something.
I am trying to prove that a PDF document contains forged signatures. If I can view the PostScript code, then I can prove that the page is presenting the forged signatures as imported images, rather than ordinary page elements. It is my understanding that PostScript code represents page elements on a host page, and that imported graphics are essentially encapsulated PostScript superimposed on that host page, similar to the way JPEG photos are imported to a website. If I could view the code, I could prove to a judge that these signatures were forged.
The type of image you're talking about is an ordinary page element.
Your understanding about Postscript in PDF and images that have been added to an existing PDF document is not accurate. Even if it were possible to prove a document was tampered with (which it probably is not), you would have to have more expertise.
You can view the internals of a PDF file using the Preflight feature of Acrobat Pro. That's what I would use for this.
You can also open a PDF in any number of editors. The problem is many things in a PDF are binary data, and are commonly compressed and encrypted. This makes it very difficult to make sense of much of it.