Not deployed/installed - Check to make sure Read&Write for Google Chrome was installed from the Chrome Web Store. If deployed through an organization, ensure it was deployed by a Google administrator
Permissions - The Read&Write for GoogleChrome toolbar will not appear in Google Docs unless permission was accepted by the user. If the extension was installed, but the user did not grant permission, permission will be requested again each time the user opens a Google Doc. You can follow the instructions in Allowing or removing permissions to remove and then grant permissions to the extension to ensure that permissions have been granted properly.
Wrong Chrome profile/not logged in - Chrome extensions are associated with a Chrome user account. Click the Chrome account name tab at top right of screen and make sure you are logged into Chrome and also logged in under the correct account. For example, firstname.lastname@example.org instead of a personal or other account
Account not syncing - We also recommend checking to make sure that your Chrome account is syncing. In the upper right corner in Chrome you should see your account name on a tab (you won't see this on a Chromebook) if there is a yellow triangle next to the name, click the icon and it will prompt to sign in again. If you don't see a yellow triangle, please read Sign in or out of Chrome and follow the instructions in Option 1 to disconnect the account using the instructions for Computer.
Use by default not selected - Check to make sure that Read&Write for Google Chrome is associated with docs. Please read Use by Default