There 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 Virtual Data Room;
choose the report titled "Over files and folders" on the left side of your VDR;
on the second vertical section from the left (titled “FILES AND FOLDERS”), please 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 type "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: