I'm new to this board and came across your problem as I was browsing for something else.
I have the same problem with Adobe when trying to generate a pdf containing mixed raster and vector data in Mapinfo. Vector data plots--raster backdrop doesn't. Solution: simple, but just one more step. Install Ghostscript and Ghostview first. Then install a plotter/printer that supports postcript files (EPS or PS). Print or plot to "File" the postscript file. Ghostview will open it, but you will have to tweak the dimensions sometimes as this is not always automatic. In Ghostview you can CONVERT a file to a PDF (do not "save as" but convert). When you do, add the PDF extension because it does not do it automatically.
This should yield the pdf you want at any size you want. Installing Ghostscript and Ghostview is not transparent (needs pointers to directories, etc). And Ghostview will need a bit of reading and practice until you are comfortable with it.