Sibelius to Dorico

Can I open Siblelius 3 files in Dorico?

Welcome to the forum, Usebius. You can’t open Sibelius 3 files directly in Dorico, but you can install the free Dolet for Sibelius plug-in and then export your Sibelius scores as MusicXML, and open those in Dorico. You can download the Dolet plug-in for free here. (You need the Dolet 1 plug-in for Sibelius 2.1 to 5.)