How to create a PDF from a DOCX without flattening PNG images?

Question

What I want to do is to create a manual that looks like it has its illustrations roughly painted onto parchment.
I've created a .docx document in Word that looks correct - the images in it are PNG files with transperancy around the edges so if a background is put behind them, it looks like it's painted onto that background.
However, when I use Adobe Acrobat 9 to try and convert this to a PDF, all the images in  the  resulting PDF file are flattened and lose their transparency.  This isn't immediately obvious when the page background is left white, but as soon as the background is set to the 'parchment' image, it's obvious that the transparent parts have been flattened into solid white, which naturally looks hideous.
Is there anything I can to do maintain the transperancy of the images in the DOCX document when converting it into PDF?

Answer 1

While I haven't exactly managed to find the answer to my question, I've found a workaround that gives me the look that I want.
Instead of adding the 'parchment' background in Adobe Acrobat, I already add the background (as a Watermark) in the original Word 2010.  Although I think the images still get flattened, they get flattened into the parchment background so it doesn't actually matter.
Solved now!