If you're talking about an eSignature implementation that would work inside and outside your intranet then you are attempting something too ambitious. If you need eSignature type functionality I would suggest something like DocuSign.com. You definitely want to use an SaaS solution if you need external users in a future release. DocuSign now has a feature that allows document attachments btw. If you're just looking for a way to post documents and track viewing then I would suggest something like Acrobat Pro generated and eSigned PDFs that are posted on an Apache HTTP server. Turn extended access.log logging on and for intranet you could implement something like CA's SiteMinder for NTLM authentication and log the NTLM username/domain in access.log.
There's a free version of the expensive OmniFind product by IBM available with a little bit of Yahoo branding (which can be removed). You can't really integrate it easily with local search but I would assume that your users know whether they want local or shared documents. If you need security/permissions around people being allowed to access certain documents you're going to need to buy something. Otherwise try: http://omnifind.ibm.yahoo.net/