If you mean like they were printed on clear film for the page behind to show through? That cannot be done on screen.
Noooo. Thank you!
What should a 'transparent page' show on screen? The electronics inside your monitor?
It would be nice if it automatically showed 'the next page', slightly transparent. But that's not an option in PDFs. So if you want to mimick what happens in the printed version, you could copy the entire next page (*), apply some transparency to it, and place that in the background of the "transparent" page. You can use Transparency on the copied page to make it lighter, so the text on the "top" page is still readable. This is the right hand page, copied underneath the left hand page and set to 20%:
(*) And if you already have a complete PDF, just use that.