When another user sends you open a Proof URL and you open it in your browser, it launches the Proofing Viewer in Read Only mode. Before you can work on the proof, you need to identify yourself by subscribing to it.

NOTE Before users can subscribe to a proof, its Subscription setting must be enabled (see the section "Allow Other Users to Subscribe to the Proof" in "Configuring Proof Settings").

 To subscribe to a proof:

1. Click Sign In at the top of the Proofing Viewer. 
2. Type your email address in the Sign in box that appears.
3. If you are not a reviewer on the proof nor a user of Workfront Proof, type your display name.
   Or
   If you have a Workfront Proof password, type it (whether or not you are a reviewer on the proof).
   Depending on the proof sharing email settings selected by the person who shared the proof, you might need to follow validation instructions in an email sent to you via email.
   Your role on the proof is Subscription, which is set on the Proof details page for the proof. For more information about setting roles for proofs, see "Configuring Proof Settings."

This was previously called "Subscriptions."