To the web design purists, this is a simple question. I no case should you open up a new window, because it breaks the back button functionality and may disorientate your viewers. However in my tests I have come up with a few rules that on our b2b business site ensure that our customers have the experience they want.
My first rule is with pdfs. Most pdf’s on most commercial sites are brochures or white papers that tend to be saved or printed for later consumption. If this is the case then open these up in a new window. That way it seems that our customers actually get less disoriented, and they can decide what to do with the pdf later. Personally I think that there are a few reasons this works. The first is mentioned above, the second is that pdf’s open up in a plug in that doesn’t have the traditional look of a web page and in fact has it’s own menu bar in most browsers. The last reason is that pdf’s aren’t web pages. Usually the only navigation open to you is the back button. So in that way it is easy to get disoriented if it is not isolated.
My second rule is a simple one, and to a large extent it is being superseded with newer technologies, but if you are not using ajax, and want to add in supplementary information, but still allow the main page to be viewed I would recommend a new window or a …wait for it…pop-up window. I know, I know, no one likes pop-ups, but is that really the case. If I ask for more information and it happens to be in a pop-up, I really don’t mind, and that has proven to be the case with our customers too.