Give the means to a user to undo its signature

Once a user has signed the pdf, he should have a mean to undo his action: that means put the pdf back to the state it was before. In my opinion, snapshotting/versionning is not the good option for this. What I suggest is that before updating the pdf file with the stamped and signed one, the previous one is attached to the document in the "files" schema, with a file name that would be something like "PREVIOUS-NAME-Before-aescaffre-signing-2011-04-15-01-45-pm.pdf".
That way, the user could easily : delete it if he doesn't want the older one to be still available, or download it to repalce it on the main content property. And this would have not link with the versioning cycle of the document, as well as it would be compatible with multi-signing. (more files added).