Compressing a PDF to smallest size changes layout

Hi,

I have a PDF doc that's only used online, it's 7.7mb and I want to compress it for easy email. 
if I compress using the app on medium setting it only reduces by 1mb. 
I selected the high compression and it reduced to 804kb which is perfect but it changed the format of my PDF. 
It seems to break each section into collapsible sections and places the images above rather than in the doc. 

Any ideas how I can reduce the size without the layout / format change? 

thanks