How long have you been working with this approach to document editing? We initially used Google Docs to edit simultaneously, but there was no way to track who changed what and when, so we decided to switch to procurement contract management software. Before choosing a platform for this, I read information about CLM features on http://zefort.com/blog/procurement-contract-management-software-the-ultimate-guide/ , you can check it out. All edits are made in one place and the entire history of changes is stored with all the information about who added what, and you can also go back to any version of the document. We set up granular permissions so that each department can see what they need without unnecessary information.