Event Log Files can be used to find the Documents or Files viewed by the users in Salesforce.

1. Find the Event Log Files with ContentTransfer as the Event Type.

2. Download the File and filter TRANSACTION_TYPE as VersionRenditionDownload.

Reference Article:

https://developer.salesforce.com/docs/atlas.en-us.object_reference.meta/object_reference/sforce_api_objects_eventlogfile_contenttransfer.htm