PDF Document inSpector is a browser of a PDF document's contents. If you're not doing something pretty down-and-dirty with PDF, I can't imagine how it would be useful to you. On the other hand, if you are working with the innermost bits of a PDF file (like I was with Cheap Impostor), I can't think of any other tool out there that would help you figure out what's going wrong.
Well, you run it, and then open a PDF file. A pretty Spartan window will pop up showing you the top-level objects of the file in an outline view. Click on the "disclosure triangles" to open up an item. It will all look really cryptic if you don't already have an in-depth knowledge of PDF document format.
