How to attach a file to the current page with a plugin

Hello everybody! I write my diploma thesis! And I have a problem. I want to attach a file to a page of the xwiki. This should happen automatically - this means without any intervention of a user. You can attach a file over the GUI and I want the same functionality in my plugin. The file should be loaded from the folder and attached to the page over the plugin and velocity. A batchscript should update the wiki every hour, when some files in a given folder have changed. The class "Document" in the package "com.xpn.xwiki.api" has a method "addAttachment()", but I have the problem that this method is protected. Thus I cannot attach a file with a self-written plugin. I don't find any information about this context in the documentation. Has anyone a solution for my problem? Could this person please send me the coding or the link where I find the documentation/ information to solve the problem? Please please help me! I have to implement this functionality but I don't know how. My diploma thesis is very important for me and I'm desperate!!!