Word Creates Multiple PDFs
Problem
You File>Print, Save as PDF and it creates several PDFs from the same Word document.
Relevant versions: Mac OS X and any OS X version of Word—Word 2008, 2004, and X, as of the time of writing.
Solution
Word 2008 only: It's been reported that using the File>Save As, set Format to PDF feature, creates a single file PDF.
All versions: In OS 10.5 (Leopard), you can combine PDF files using Preview. Check Preview Help for more detail.
In OS 10.4 (Tiger), or earlier OS versions, use a utility such as Combine PDFs or PDFLab to merge the multiple files. Both donationware, both tested and recommended by MVPs.
Explanation
Whenever a section break in Word is used to change margins or page orientation, Word sends a separate print job to the printer. Each print job results in a separate PDF file. Sometimes you can edit your file to get rid of these section breaks, but it probably isn't worth the trouble.
Upon seeing this without margin or orientation changes, one newsgroup poster reported that deleting and re-entering the section breaks fixed the problem in his document. Other people have seen this with plain page breaks.