I paid a freelancer programmer for an app to tun my clinic. He got about 95% of the project done, but then got a job elsewhere and vanished into thin air, along with my source code... So, I have a semi-working program and I need to finish it. How can I recover the source code (Visual Studio, C#) to a point I can finish what I need and then recompile it again? Is this possible? I'm willing to buy/pay...
Consider also JetBrains dotPeek that is free, decompiles .NET 1.0-4.5 assemblies to C#.
Has support for .dll, .exe, .zip, .vsix, .nupkg, and .winmd files.
To answer your question "Can I end up with the original source code in a way I can finish the coding of the missing items and recompile again?": if it runs on your system, it means you have all the dependencies needed and you'll be able to decompile to a state where you can edit and recompile at will.
I don't know about Reflector, but with ILSpy, you have the option in the File menu to "Save as..." and you can save a .csproj or a .vbproj (this can be done because the intermediate language of .Net can round-trip to both languages; so even if coding was in C#, you can roundtrip to VB if you wanted).
There are many free and paid utilities out there that aim to decompile .NET applications.
Personally I use .NET Reflector - which is a commercial application with a 14-day free evaluation version.