Whether you want to share a Google Doc with a colleague so you can work together, or you want to kick a coworker off a project entirely and unshare a Google Doc, it's easy to alter the permissions on a Google Doc.
When you unshare a Google Doc, anyone you've unshared it with will have their permissions revoked immediately. This means they won't be able to edit or comment.
If you've totally locked the document, they'll still be able to read it until they refresh the page. But once they do refresh, their access will be gone.
How to unshare a Google Doc
1. Open the shared Google Doc.
2. Click on the blue box reading "Share" in the top right corner, and then, in the bottom right corner of the popup window, click "Advanced."
3. On the new popup menu that appears, to simply unshare the Doc entirely, click the "X" next to the name of each person you want to remove access from.
4. If instead of removing someone altogether, you'd rather change the person's permissions in the Doc, click the pencil icon beside their name and email, and then select their access ("Can view," "Can comment," "Can edit," e.g.).
5. Click "Save changes" and then "Done" to confirm the change or removal.