Microsoft Office export to PDF feature greatly increases file size

I created a PDF out of a Word document, using the export feature in Word, and uploaded to a website.  The website complained that the file could be no greater than 500kb.  When I checked, my Word document was a mere fraction of the size of the PDF.  Through testing I learned that by using PDFCreator (, an open-source PDF printer, my PDF came out comparable in size to the original Word document and allowed me to upload it. I have no idea why this happens, but found it interesting.

(This was done using Office 2012)