When I open a DNG file , make enhancements to the photo in Photoshop and go to save the file Photoshop is forcing me to change the file format to tiff or jpg etc. DNG isn't listed in the save as menu.How do I keep the file in DNG?
You don't. DNG is Digital Negative in other words the same as a raw file cr2,nef etc.
If you want to keep enhancments within the DNG it can be done in Bridge using Adobe Camera Raw.
Is the DNG truly raw camera data, or is it rendered data saved as DNG?