If the website looks like it was built in 1998 and has flashing "DOWNLOAD NOW" banners, close the tab immediately.

Using an online EXE decompiler is relatively straightforward:

Short workflow for a safe quick check (example)

Open-source tool by the NSA; arguably the best free native decompiler available. Allows you to view, edit, and recompile .NET code directly. ILSpy .NET Assemblies A popular open-source .NET assembly browser and decompiler. IDA Free Disassembly