Mac IWAD

Do doom IWAD files from pc transfer to mac?

Yes, but you need a source port to play them.

Same IWADs no matter the operating system (fan-made console ports, too; like the Nintendo DS one). All you need is an engine to run it.

Chocolate Doom and PrBoom run on Mac OS X, but I'm not really familar with other choices available.

And id Software also released a port to the Mac. It's from '96, so I don't know if it works properly on the current OS.

It won't run on Mac OS X, unless you're on a PowerPC and have Mac OS 9 as well (also assuming that Mac OS 9 can use it).

The IWADs included with Mac Doom, Doom II, and Final Doom are identical to the IWADs included with PC Doom.

In addition, the official Mac Doom port is compatible with all PWADs that the original Doom.exe/Doom2.exe is compatible with. Of course, if you want to run WADs which use DeHackEd patches or custom graphics, you need the appropriate tools (The Doominator for DeHackEd patching, and...uh, I think the program to expand the graphics in a wad was called WAD Expander?).

With that said, if you're trying to run Doom on a Mac, I recommend getting either PrBoom or PrBoom-Plus, since they have nice, stable, precompiled Mac binaries. Some other Mac-compatible ports include Doomsday Engine (fancy OpenGL-based 3D graphics), Legacy (don't bother, the Mac port is pretty incomplete), Chocolate Doom (you'll have to compile it yourself), and Eternity Engine (you'll have to compile it yourself).

(also assuming that Mac OS 9 can use it)

Indeed it can.   :>