PDF not reducing in size

[ssamanen]

I'm trying to optimize a 700 MB PDF file with many embedded raster images.  The image quality degrades, which is acceptable, but the file size isn't getting any smaller no matter what I do.  I even lowered the compression setting to 20 dpi, which looks awful, yet the file size remains exactly the same after re-saving.  Any ideas?

[Test Screen Name]

Try using Audit Space Usage before and after compressing. It may point at an issue (or not). 

[ssamanen]

Thanks!  Not sure what I'm looking at there, other than that 94% is document overhead.  What kind of issue would be correctible?

[Test Screen Name]

Document overhead isn't usually reducible. Shows the images weren't much of the file. But what can you tell us about how the file was made? Please name all the apps involved. Maybe there is an alternative way.

[ssamanen]

It's 9 artboards, 11x17 each.  The artwork was originally exported from Vectorworks as embedded bitmaps, then I drew small logos and illustrations on top, along with a few bitmap textures, which I flattened and cropped using Flatten Transparency, thinking those were a major source of the bloat.  I guess they're not!

I don't know what document overhead really is, so hard to know how to reduce it.  Copying and pasting all the objects into a new document doesn't change the file size much.

[gary_sc]

Is there a reason for you to turn the vector image into bitmapped images? Bitmapped images typically require a LOT more storage space then vector images.

Can you take one of the drawings and save it both ways to see what the difference is?

[ssamanen]

The largest images were exported from another artist and he had them in Vectorworks as bitmap images, not sure how they were originally created, but I don't have those as vectors.  The drawing is in 1/8"=1'0" scale, so I added textures for small pieces at full scale, which I thought was making a big difference.  But even after embedding them at smaller size there was no appreciable change in file size.

I'm still just puzzled that even with extremely low-res high compression, the file size was still enormous.  You'd think it would've made the file smaller, which is what made me think something was wrong.

Is it possible that the bitmap images are what constitutes "document overhead?"