Possible to use a .dll on Linux

You could try extracting the ar file (Debian packages are ar files, fwiw) and run file on the contents.

You're not going to be able to use Windows DLLs without translation. The only DLL files that I know of that work natively on Linux are compiled with Mono.

If someone gave you a proprietary binary library to code against, you should verify it's compiled for the target architecture (nothing like trying to use am ARM binary on an x86 system) and that it's compiled for Linux.

That being said...good luck. I hate programming against third-party libraries where I have the documentation and the source.

.dll files are usually Windows shared libraries. (It's also possible that somebody on Linux has built a regular Linux library and called it .dll for some reason.)

It's possible you could link against them using Wine. Support for this was once in there as experimental - I don't know its current status.

Recent development may have changed the situation: There is a loadlibrary function for Linux available, that makes it possible to load a Windows DLL and then call functions within.

So, if the .dll file you have actually is a Windows DLL, you may find a way to use it in you software.