Does Evince (Document Viewer) have a plug-in system?

Does it have API? If not, whats the simplest PDF viewer that does?

What I do want to create: Maybe annotations (which could be shared via an external file) or creating hyper links to Wikipedia. That sort of thing. You could even have remote control where the viewer could sync many open documents across different computers all at once. Not sure yet.

In principle evince can be controlled through its dbus api. An example of its application is the SyncTeX plugin for gedit, which allows easier editing and browsing of latex source files in combination with evince. On the other hand, the dbus api itself has been found to change sensibly from gnome 2 to 3 and it's somewhat hidden so you'll have to dig into the evince source to find the exposed methods.

Concerning annotations: as of version 2.31 evince supports adding (but not deleting) annotations. This feature is currently broken in evince 3.2 (the version shipped with Ubuntu 12.04) due to a regression but a fix has been released upstream.