Could someone tell me the default font that DirOpus uses.
Thanks.
Font defaults depend on the version of Windows you are using and what Windows is configured to use. (Also, if you copy the config to another machine, it'll keep the font settings from the old machine unless you change or reset them.)
You can see most of the fonts Opus uses under Preferences / Display / Colors and Fonts, and if you need to reset it to the defaults for your current OS you can use the File menu in the same window, when viewing that page.