There are two main ways to effect the file size of a scanned PDF. The main way would be to lower the scan resolution. For most black and white documents you should not need more then 100dpi to get a good quality PDF. If the file size is still to large, next to the PDF file type option should be a Set button. When you click Set, there will be radio buttons for PDF Compression. The default is standard, and if you change it to high, it will reduce the file size.