Reducing File size of PDF file

I have a number of files  which were prepared in Corel Draw which I would like to post online.  The designer has supplied the PDF versions of these files, however, the files sizes are too large for web usage. A 8 pg document is 5Mb. I have tried reducing the sizes by compressing in Acrobat;  importing the PDFs into Corel Draw and re-creating PDF files with reduced resolution; recreating the PDF without the bitmap images (there are about  10 images)..yet the file size of the PDF does not change significantly.

What else can I do to reduce the file size of the generated PDF files?  

The files are newsletters, so most of the content is text and a few shapes and lines.