"Reduced Size PDF" results in the exact same size PDF

[Nora_Nora]

Hello, 

I am in the final stages of editing my design portfolio which must be laid out like a book with spreads and table of contents etc, and which is meant to showcase detailed digital drawings that took months to produce. Thus, I always struggle to reduce the file size without sacrificing the quality of the images. This time around, I have exported all of the artwork into JPG and PNG before placing into inDesign and my resulting PDF is 20.5MB (instead of 40+MB which it was when I had been linking to the working files).  

However, I was hoping to reduce it still further,  ideally 15MB or less. I used the Acrobat feature Reduced Size PDF, but the resultant "reduced size" PDF is the exact same size as the original (both are exactly 20.5MB).

Any suggestions for how to reduce the file further --either in Acrobat or elsewhere? Is there a reason the Reduced Size function is not doing anything for this document?  I have had great success with it on occasion.

P.S.

Also, I often have trouble truly flattening PDF documents (especially heavy artwork ones exported from inDesign or Illustrator).  Though I "flatten" it seems to somehow retain layers which prevent it from printing on the large format plotters. However, I don't usually want to export to an image file in these cases because it will compromise the very subtle vector linework. Is there a way to remove all layers while retaining vector art and/or text fonts?

Thank you!

[Test Screen Name]

"I often have trouble truly flattening PDF documents (especially heavy artwork ones exported from inDesign or Illustrator)."

What do you mean EXACTLY by "flatten"? It's used to mean at least four quite different (and contradictory!) things.

" Though I "flatten" it seems to somehow retain layers which prevent it from printing on the large format plotters."

(1) flattening layers is one possible meaning of flattening, not the most usual one.

(2) layers should have no affect on file size or whether something prints. Maybe it's actually something else.