Using WORD 2010, how do I convert a WORD file to a PDF file and keep the same PAGE SIZE (A5 in both). When I tell WORD to convert to PDF it changes the page size from A5 (half page) to A4 (full page)

I have not done this before but, once you click on the Acrobat ribbon, then click on "Preferences" in the Create Adobe PDF section. In the subsequent menu, click on "Advanced Settings"...then define the Default Page Size to the correct size of the A5 paper near the botton of the menu. Then "Save As..." (your choice).

Hope this helps.