Business-Suitable Document Authentication System?

ram.loss writes "The company I work for has decided to go paperless for all memos and internal correspondence. In addition to the central administration, the company has three more or less autonomous, physically separated divisions; that means we do not have a common IT infrastructure across all of them. Since I am the only resemblance we have to an IT department at my division, I have been commissioned with evaluating the available technology to manage and authenticate all correspondence, although it is not my area of expertise (I have a CompSci degree, but for many years have specialized in transportation modeling software). My initial thought was to use a document management system like Plone (this is the system I'm familiar with); from what I have read, that would take care of the management part, but what about authentication? We need each document to be signed, and a fully auditable system that keeps track of who signed what document, who received it and when. It also must take into account the handling of external correspondence in the future, where a recipient outside the company must have the means to return an authenticated document as a response. I'm aware that I'm leaving out a lot of details, like how the documents will be signed, the legal implications, etc., but for the time being I'm only interested in the experiences of the Slashdot crowd with such systems, and hopefully finding out enough information to hand over the matter to (or hiring) somebody more qualified, once I know what to look for. Has anybody out there used a similar system? Am I in way over my head?"