If you get an email from someone wanting to share a Google Doc with you, do not open it. In all likelihood, you are the target of a widespread phishing scam to get access to your account data. Clicking on the "Open in Docs" button will send an email to everyone in your contacts list, as well as bringing you to a page that will ask for access to your account. If you already opened it up, go to your Google permissions page and revoke access for the app called "Google Docs" and immediately change your password.