When you print a PDF document using the Print dialog in Adobe Reader on Windows, you might find a few Page Scaling options. Here is what they mean:
None: Prints directly without applying any scaling. Generally, not a good idea to use. Scaling the document to fit the size of the paper is a better idea.
Fit to Printable Area: This is the most useful option and what I use by default. It tries to expand the page content as much as possible to fit the paper. When used to print multiple pages per sheet, it adds a border around the individual pages.
Shrink to Printable Area: I have no idea why one would need this option. It shrinks the content by quite a bit. So, your content looks smaller when printed. When used to print multiple pages per sheet, it adds a border around the individual pages.
Multiple pages per sheet: Useful to print multiple pages per sheet. Does not add a border around pages. Surprisingly, I have found that it prints pages a little bit smaller than Fit to Printable Area.
Booklet Printing: Prints 2 pages per sheet in the form of a booklet. Beware that it prints the pages in an order such that you can stitch up the center of the pages to form a book. Unless you will be needing this, this is not useful and better avoided.