Digital Sender sending large file sizes.

We currently have our 9200C Digital sender set to send out images as
PDFs. I checked the mfps configuration software (ver 4.7.6) and the
settings are for a resolution of 150 dpi and Standard (which are the
default settings). According to the user manual, this means the PDF's
should be about 500K in size. However, they are showing up as 4.0 MB
in size and they are freezing our user's Outlook programs on their
workstations, when they try to forward the documents. I also checked
the settings on the unit and they are set to standard size and 150
dpi. It was set to color, but changing it to black and white made no
difference. Any idea why this is occuring?