Hi,When turning DWGs into PDFs for issue the file sizes become
massive, too big to send in an email. I find this strange because the
orginal DWGs were tiny. For example drawing M/002 was 272KB as a DWG
but when converted it became 2.45MB. Any ideas why this is and how I
could make them smaller?I am using AutoCAD2004LT.Thanks

Normally PDF files created with smaller or equal file size, but if it
increases steep then there must be extensive x-referenced drawings
associated with your "main" drawing, the drawing size to be converted
should be main drawing plus x-ref drawings, if this is the case, there
is no way to convert into smaller PDF file size and still keep all the
drawing information, what I did to resolve/reduce the file size was try
to convert drawing(s) into PNG image, and send out PNG file directly,
get a try with the converter software, I found free download from here:
http://www.autodwg.com/DWG2Image/

It depends on how you convert the DWG to PDF. There are many PDF printer drivers (some of them really free of charge) and each uses a different method (e.g. converting drawings texts to vectors).
 
A more effective way of publishing a DWG drawing is using the DWF file format. Besides a smaller file size you'll get some other advantages - see:
http://www.cadforum.cz/cadforum_en/qaID.asp?tip=2027