Foxit PDF Preview Handler for XP is an add-on designed to work with Outlook. Its purpose is to give a preview of PDF attachments. You'll notice that when you click on a PDF attachment, you get a message telling you that you don't have a previewer installed. This add-on just solves that.
This version has been developed specially for Windows XP because this operating system doesn't have a preview host just as Vista and 7 do. It uses some Foxit Software source code, hence the name.
You don't need to have the Foxit Reader installed on your PC for this add-on to work. Actually, you don't need a PDF reader at all, as it renders all the pages in the document on its own. It has the main features for reading like zoom, bookmarks tab, skip pages, page rotation, and more. So, for an Outlook previewer, it's fully featured.
Even though the official website states it has been designed for Outlook 2007, it works perfectly well on the 2010 version of this mail client packed with Office.
So, if you are a Foxit Reader user, this is a great tool. And if you are using Adobe Reader, just make sure you have the latest version of the program, as this will install a previewer by default.
One more thing to consider is using an up-to-date AV software, as previews in mail clients are known to let malware in your system. But I wouldn't worry so much about that, because the main mail servers scan attached files.