Xsane works quite well, even if you want to scan a multipage document into a PDF. Just select ‘multipage’ as the target:
and then this window will pop up, where you can select an output format; the default is PDF.
I had a 17 page document to scan, which I (foolishly, perhaps) did at 150dpi. That resulted in a 30MB PDF, which was a bit larger than what I was looking for. So I changed the export format to Postscript, and then used ps2pdf to create a compressed PDF like this:
ps2pdf -dUseFlateCompression=true input.ps
That PDF clocked in at 4.5MB – not bad as a compression ratio! It’s possible to compress the PDF even further by using ‘target devices’ like so:
ps2pdf -dPDFSETTINGS=/screen input.ps
/screen is the most heavily compressed ‘target device’, and that gave me a PDF of 1.5MB, but pretty crappy quality. There are more target devices, and a lot more options, some of which are outlined here.