Database file for ACDSee
DTF is a file extension for a database file used by ACDSee. DTF files contain a database of thumbnail images used by ACDSee. DTF files and their associated DDF files can be deleted if ACDSee is responding slowly. DTF files are used by ACDSee but aren't directly viewable with the application.
Learn more about .DTF files:
Visit the ACDSee web page.
Read about Thumbnails at ITKnowledgeExchange.com.