So what you are saying is you would like to insert all pages of an external PDF to form the chapter of your publication? I think by default the closest you can get to that is to place one page from a PDF as an image. With some fiddling you could create a customisation to loop through all pages of the PDF and place them but that is not "out of the box".
I like this idea though, and it would certainly be useful in many scenarios. You could promote this as a "product enhancement" through PTC Support?