There are two ways to track activity over a file depending on your needs:
To check whether a specific document has been viewed by specific users.
To check whether the documents have been viewed at all, by any user(s).
To check whether a specific document has been viewed by specific users:
Go to the Reports tab at the top panel inside your data room.
Choose the report titled Over files and folders on the left side.
On the second vertical section from the left (titled FILES AND FOLDERS), choose your specific file.
In the Action filter, select the option File viewing.
In the Author filter, select your specific user.
To check whether the documents have been viewed at all, by any user(s):
Navigate to the Reports section.
Select the report Files and folders.
In the Files and folders section, select your specific file.
See the number next to the action File viewing which corresponds to the number of times that a document has been viewed. If the number is 0, the file has not been viewed yet.