Use .NET Framework DLL in .NET Core

In principle, yes. The DLL format of CLR , or more commonly called .NET (although technically an error), is universal and works in any environment prepared for your use. this includes grabbing something from the .NET Framework and using it in .NET Core . There would only be a difference to .NET Native that has a native format.

This does not mean that everything will work. What's part of .NET Standard will work, since what's specific to an implementation it will not work. You will not be able to use specific things for Windows. Even .NET Core 3.0 supporting WinForms and WPF does not mean that it will run on Linux, unless someone uploads them to this operating system, which is not simple, especially in WPF.

So the executable format is not a problem, but not all code is universal.

See more at What are the differences of ".NET"? .