I'm not really sure what you're aiming to describe, and don't have .pdf as a Paste Special option on 2010/Windows. It sounds as though Word might be resizing the spreadsheet to fit the page margins – it's only trying to help.

Experiment with resizing the table in Excel before you paste it as HTML. You could also see what happens when you select the table and try Autofit, or select it and change the font size.