I've had this problem for a while, both in Jaguar and Panther. Can anyone reproduce this problem?
1. Mount an SMB volume on your Mac (in my case, it's a shared directory on an XP Pro box. The disk is NTFS, I haven't tried FAT32 format).
2. From the SMB volume, drag any PDF file over to either your desktop or another Finder window.
No matter what I try, I can't get the file to copy over (this only happens with PDF files, all others are fine). I couldn't find any mention of this on the Apple discussion forums, so I'm guessing it may be something specific with my setup.