How are you trying to copy them? What is happening that makes you think Windows cannot handle the DNG files. I'm using Windows 7 and have no problem with them.
I'm using Allway Sync. I must admit that their error messages were ambiguous.
I'll try Easy Transfer and see if that works unless you can suggest something better. I am going from a Windows 7 computer to a windows 8.1.
Thanks so much for your help.
To me, it's not really clear what you're trying to do. All that should be necessary is for you to install Lightroom on the Windows 8.1 computer and then put your catalog that you have been using and your images on that computer. If the images are still in the same folders, and on the same drive, then all you should have to do is open your catalog and go to work.