Many file types use DSF format, but when it comes to dwg to dsf conversion, it is probably related to Corel Designer or even the previous Micrografx Designer, which are actually the only tools that can save to this type of DSF format. Depending on the version you need, you will either need Corel Designer or the old Micrografx Designer, the latter can be still found on abandonware websites.
Updated: September 19, 2023