All of the source control applications already mentioned do a good job of tracking changes for source code, and the resulting binaries. However, there are other applications that have been designed expressly for managing documents. At the company I work for we use Livelink from Open Text (disclaimer: I have absolutely no financial interest in Open Text - I just use their product). FWIW, we also use subversion for managing our internally-developed software. Everyone, from our CEO on down, uses Livelink to store documents. We literally use it to manage all of our documents.
Livelink stores all of your documents into a database, and provides access and version control on those documents. You have the option of either a web or windows explorer front end that is easy to use for nearly everyone. The software allows you to search through document contents; Create shortcuts to related documents; Provides an interface into Excel, Word, and Powerpoint; and looks to end users like an ordinary file system. You can even set up alerts that send you an email when a document changes, or there is a new document added to a specific folder. If you're truly a glutton for punishment, it has an api that you can use to customize its behavior or integrate into other applications.
There are other document management applications available. I know of, but have not used documentum (spelling?), and I suspect that Xerox and perhaps Adobe also provide document management systems.
The bottom line is that you should try to use the tool that is appropriate for the task. As the old adage goes: When your only tool is a hammer, everything begins to look like a nail :-)