By clicking the Security option, you will open a window with Document system information. Here you can find information about who created (or edited) the record and when, or what the record validity is.
Only the users with special permission can view the records. You can lock any record that you have permission to access and prevent other users from editing it. The record can be unlocked by you or an administrator.
Invalidating a file will make it invisible in the Documents but it will remain saved in the CRM. If you wish to show even invalid files in the Documents, click the Show Invalid button which can be found in the file and folder list header.
If you have a lower monitor resolution, you can find the Show Invalid option under the Other Filters button.