Ah, OK.
So to do this you will need to track the uploads folder with your CVS. This is where the documents are saved. You will need to install the command line version of your CVS. Then create an after save logic hook that would commit the new changes to you repository in command line. You could use the exec function do achieve this. http://php.net/manual/en/function.exec.php
To revert the changes you could then use tortoise or if you could add new functionality to SuiteCRM so that it reverts a document back to a previous version.
To be honest, It seems a little over kill to use SVN. SuiteCRM keeps entire revisions in the uploads folder. So it would be far easier just to change the document_revision_id field back to an earlier version. This could be achieved using a custom controller action which could be added in a custom view via the meta data folder.