DTF files are database thumbnail files used by ACDSee. They contain image previews stored to speed up loading. ACDSee can view DTF files. But there is no way to convert them to other formats. DTF files are also temporary Domino server data. If not removed automatically, delete them manually after shutting down Domino. They are validly named like s054321.dtf. Without proper software, you’ll get “How do you want to open this file?” Windows alerts. Use ACDSee or Symantec Q&A. They associate with and open DTF files. Many share DTFs without instructions. So we offer guidance on handling them. Update any software that gives “cannot open” alerts. Scan DTFs to check for viruses too.
Symantec Backup Exec
IBM Tivoli Storage Manager
Various Database Programs