We’ve had reports from a few users who are unable to open PDF files from within their accounts through the Web Folders interface.  After some research we’ve found that this is a known problem with Web Folders for XP users who are also running Office 2007.  (Note- some users have reported that the problem effects Office 2003 as well and that this fix solves the problem.)

Microsoft has released hot fix KB943337 that should resolves the problem for most users with webfolders (also known as webdav) and PDFs. You must request this hot fix as it is not part of their automatic update process.

The link to the fix on the Microsoft site can be found here:
When reading the directions for the hot fix please note the section requiring that a previous webfolders update, released May 18, 2007 (907306) be installed prior to installing this current hot fix.
Thanks to our friends on the Adobe forum for finding a solution to this problem, which seems to only effect XP users.