I scanned a rather longish document (241 pages), which resulted in a 101.7 MB document. I needed to get the file size down, but couldn’t find a decent way. 

Finally, after quite a bit of googling, I found this link. I don’t know why, but it worked. It got that 101.7 MB document down to 72.9 MB, which is a 28% reduction. I’ll take it.

pdf2ps input1.pdf input2.ps
ps2pdf input2.ps output.pdf