So, me and a few buddies rented a small office space two weeks ago, we figured we'd need a "base of operations" while we raise a few affiliate sites/networks and keep on sharing link-building opportunities. There are 7 of us right now and we have a varying number of collaborators living in different time zones as well. We use G Drive and Trello to communicate, but as the number of ongoing projects rises, I feel like we'll need something more robust before long.
This got me thinking of installing a filing system software, an app that we'd all have access to and one that will allow us to track which doc has been changed recently and by whom. We don't prepare the invoices ourselves, actually, we hire a contractor that does the math and sends them to us first as a PDF. We also scan the incoming invoices and send them to her, so having an app that can automatically route, separate, and name the docs/PDFs would certainly save us some time. Not to mention, make the process far more error-free than it is now...

Any recommendations for where should I start looking for that type of "office" software"? Thanks!