sign in to iCloud with an Apple ID
Shared documents are stored in iCloud, and to access them you must sign in to iCloud with your Apple ID.
If you’ve ever purchased something from the iTunes Store, App Store, Apple TV app, or Book Store, you have an Apple ID. If you don’t remember your Apple ID, or you know you don’t have one, tap one of the links below the iCloud sign-in fields to either create an Apple ID or retrieve your Apple ID or password.
Do one of the following to sign in to iCloud:
On a Mac: Choose Apple menu > System Preferences, then click iCloud.
On iPhone or iPad: On the Home screen, tap Settings, then tap iCloud.
On the web: Go to iCloud.com.
On a Windows computer: In Windows 7 or later, click the iCloud app or tile on the Start screen, or choose iCloud from the Start menu.
If you can’t open the document, it’s possible the email address or phone number used to invite you isn’t associated with your Apple ID. Sign in to iCloud with your Apple ID, then follow the instructions to verify your email address or phone number and associate it with your Apple ID. Afterward, sign in to iCloud using the primary email address or phone number associated with your Apple ID.
Note: If you don’t want to associate another email address with your Apple ID, you could instead ask the owner of the shared document to invite you again using an email address or phone number that’s already associated with your Apple ID.