Pam,
Regarding file size, that is handled by your PDF generation software. If
you are using Adobe Acrobat, there are some preconfigured settings you can
look at that should help reduce file sizes by compressing images or other
means. Other PDF generating software should have similar settings.
When you make the PDF files, do you view them before incorporating them into
your website? If so, are they color or black and white? I'm willing to
guess that they are black and white. Again, this should be a setting in
your PDF software. When the output is converted to black and white, it can
reduce file size so this may be enabled by default.
In both cases, you'll probably need to consult the documentation for your
software.