BarbaraKathari wrote: We are a consulting engineering firm using AutoCAD 2008, we have recently noticed that on a number of .pdf files that some of our information is missing. Could this be because the .dwg doesn't fully regenerate before plotting? If this is the case, how do we stop it happening? If not, are there any other ideas on how to rectify this problem?

we had similar issue in our office. But the problem was with version of acrobat reader used. We are using for pdf creation acrobat 7. When we opened some drawings in reader 6 or 7, some objects were missing or we had some straight lines thro the drawing. When we used reader 8 or 9, the drawing was as expected.
So my advise is to try to open it in reader 9 if it is not just reader failure.

Please avoid using any external DWG-to-something convertes. Only AutoCAD can understand all types of entities and information inside DWG files.