If you receive or open a document and can't make any changes, it might be Open for viewing only in Protected View.
Note
Some editing restrictions are controlled by the document owner or your organization and cannot be changed locally.
Clear Read-Only option
- Go to File > Info.
- Select Protect document.
- Select Always Open Read-Only to clear it.
Update the document access mode
If you still can't edit, you can try the upper-right corner drop-down.
Select Viewing or Reviewing and switch to Editing.
Note
If you can't exit Protected View, it's possible that the document author or your system administrator has rules established that prevent editing.