Circuit Simulation File

[Cujo]

I have received a complicated logic circuit that was built in this simulator (.dig) file. https://github.com/hneemann/Digital

I mainly use this simulator for logic circuit stuff (.circ) file. http://www.cburch.com/logisim/

Is there any way to convert the (.dig) into a (.circ) file, so it can be used in Logisim?

[GlennSprigg]

I doubt it.   Within the first link you gave...
 https://github.com/hneemann/Digital
If you keep scrolling down that page, there is quite detailed dialog about the discontinuation of Logisim, under the
heading of 'Motivation'.  Maybe you should change over & try using that updated and more powerful software of theirs?