I've found that I can reduce the size of scanned Acrobat files by a factor of 4 to 12 by this technique:
1 - open the file
2 - Save As, JPEG2000 format
(this creates a JPF file for every page in the original file)
3 - close the file
4 - Create PDF, from Multiple Files
select all of the JPF files created in step 2.
check the order so it goes 1 to the end. sometimes the next to the last file will be the second one, move it down to the correct place.
It may take a while - I've had 500-700MB files that took an hour or two to crunch. You might need to dedicate a PC to this process that you don't need to use for anything else.
5 - Save the new file with an appropriate filename (default will be Binder.pdf - you can even save it over the original filename, but it's nice to leave the original in place to compare the sizes! I add an 's' to the end of the original filename, then rename it after I've deleted the original.
Let me know what results you get - this works for me in Acrobat 6,7, and 8, though 8 handles really big scanned images (14" by 8 foot engineering drawings) that 6 chokes on. If an images is narrow and wide, it helps to rotate it to be narrow and tall for the conversion, then rotate it back after the conversion is done.
Fred Wagner