Correct Answer. B. Check if another instance of the document is open Often, a document will display a locked message if it is already open in another instance, either by the same user on a different device or by another user in a shared environment.
Option A is incorrect as restarting the computer does not resolve issues related to file access if the file is open elsewhere.
Option C is incorrect because user permissions generally do not change without administrative action and would not cause a document to be locked if previously accessible.
Option D is incorrect as installing a different application is an unnecessary escalation for an issue that likely involves file access and not application capability.