You can invite anyone from your organization as a document Editor through the “Share document” dialog in the Editor window.
When on document sharing dialog, you get the option to search for specific users in your organization and invite them as “Document Editors.” You also can invite “Everyone” in the organization as a group.
If enabled, the option to “Notify People” will send an email to the invited users letting them know that they now have the role of “Document Editor” and have access to edit the shared document.
Under the “Settings” tab, you will find the option to allow invited folder Editors to invite other users (belonging to the same organization) themselves.
When someone shares a document with you, you can find that document on your Launcher window under the “Shared with me” tab.