You can only legally decompile a DLL or EXE or SYS or other binary executable, if you're the vendor of it.
If you're the vendor of some executable, you hopefully have source code. If you lost sources you should know the original programming language at least.
There are different types of DLLs, too. Function libraries, OLE class libraries, and assemblies.
We're not hackers here, we're developers. While Mike is assuming the best and only telling you, what you could find out yourself with google, this is not something to address here, if you're not talking of a VFP DLL.
Bye, Olaf.