I created a 33 Page PDF file in InDesign where I placed PDF files of AutoCAD drawings and some images. When I export it as the Smallest file size pdf, it saved 13 MB filed, which is to large. It is supposed to be less than 5 mb.
I have also worked with Autocad-generated PDF's (line art type of real estate projects). I know these Autocad PDF's are artwork-heavy and generally much larger in size than what we're used to from using Illustrator artwork. For some reason Autocad saves these PDFs in a more complicated way by breaking down the artwork into smaller sections generating a lot of micro-objects.
I found no way to compress the end result, other than to save the Autocad file(s) as raster images, hi-res if needed, and then, there is some control of the resulting file size by playing with InDesign's export settings.