As we outline here: http://forums.adobe.com/docs/DOC-1513
Adobe ExportPDF is capable of exporting high quality information, but the quality of your Word or Excel document depends on the quality of the PDF file you start with. For instance, if your PDF file was originally authored in Microsoft Word or Excel and converted to PDF using the PDFMaker functionality of Adobe Acrobat®, your PDF file contains a rich set of information that can be captured by Adobe ExportPDF. This includes relative positioning of tables, images, and even multi-column text, as well as page, paragraph, and font attributes.
If your PDF file was originally authored using simpler PDF generation methods, such as “print to PDF” or “scan to PDF” options, Adobe ExportPDF will convert any recognizable text and then use sophisticated conversion intelligence to preserve as much of the page layout as possible.
All that's to say, how closely the Word output exactly matches the PDF document you started with is dependent on the quality of the original conversion.
Please let us know if you have any questions.