Currently, Apsona templates must be stored in the Classic Documents object, as Salesforce Files (ContentVersion) are not yet supported for merge templates. However, as per Salesforce best practices, organizations are encouraged to use Salesforce Files, and we understand that all documents will eventually need to be migrated from the Documents object to Files. Therefore, we would like to request an Apsona enhancement or upgrade to support accessing Salesforce Files for merge templates, rather than relying solely on the Documents object.