For a long time I’ve been looking for a tool to annotate the pdf documents. The electronic versions of academic journals usually provide the articles in pdf format, and it would be nice to work with them like with the printed versions: underlining, making notes in the margin etc. This far, this has required the purchase of a full version of Adobe Reader — rarely anyone distributes their pdf-files with the “comment” property enabled, if not for anything else then for the reason, that to enable this property is not trivial.
A wonderful alternative seems to be PDF-XChange Viewer. It is as free as the Adobe product, but seems to be faster and lighter on the computer. The display quality at the XP I use at work is as good, and the biggest bonus is, that you can add your own annotation to the pdf file. These are saved with the file, and can be seen with any other pdf viewer, it seems.
You never know about the policies of individual companies, but it seems, that Tracker Software tries to do the same thing as Adobe, because the other versions of the program have more capabilites; they just offer more for nothing.
Downsides? Of course, there is no Linux version available, which is a pity. But for the time being, as I have to use XP at work anyway, I’ll be doing my readings (and annotations!) with this program.
Update on 2008-06-20:
I just tested PDF-XChange viewer on Wine after having updated my Debian testing distribution. Works well now, so even though there is no Linux version yet, the program can be used under Wine. No special setups in my case were needed.